diff --git a/exercises/error_handling/errors1.rs b/exercises/error_handling/errors1.rs
index 13d2724..83018b5 100644
--- a/exercises/error_handling/errors1.rs
+++ b/exercises/error_handling/errors1.rs
@@ -9,14 +9,14 @@
 // Execute `rustlings hint errors1` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
+use std::fmt::Error;
 
-pub fn generate_nametag_text(name: String) -> Option<String> {
+pub fn generate_nametag_text(name: String) -> Result<String, String> {
     if name.is_empty() {
         // Empty names aren't allowed.
-        None
+        Err("`name` was empty; it must be nonempty.".to_string())
     } else {
-        Some(format!("Hi! My name is {}", name))
+        Ok(format!("Hi! My name is {}", name))
     }
 }
 
diff --git a/exercises/error_handling/errors2.rs b/exercises/error_handling/errors2.rs
index d86f326..ea09376 100644
--- a/exercises/error_handling/errors2.rs
+++ b/exercises/error_handling/errors2.rs
@@ -19,14 +19,12 @@
 // Execute `rustlings hint errors2` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 use std::num::ParseIntError;
 
 pub fn total_cost(item_quantity: &str) -> Result<i32, ParseIntError> {
     let processing_fee = 1;
     let cost_per_item = 5;
-    let qty = item_quantity.parse::<i32>();
+    let qty = item_quantity.parse::<i32>()?;
 
     Ok(qty * cost_per_item + processing_fee)
 }
diff --git a/exercises/error_handling/errors3.rs b/exercises/error_handling/errors3.rs
index d42d3b1..d831801 100644
--- a/exercises/error_handling/errors3.rs
+++ b/exercises/error_handling/errors3.rs
@@ -7,21 +7,19 @@
 // Execute `rustlings hint errors3` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
+use std::{fmt::Error, num::ParseIntError};
 
-use std::num::ParseIntError;
-
-fn main() {
+fn main() -> Result<(), ParseIntError> {
     let mut tokens = 100;
     let pretend_user_input = "8";
 
     let cost = total_cost(pretend_user_input)?;
 
     if cost > tokens {
-        println!("You can't afford that many!");
+        Ok(println!("You can't afford that many!"))
     } else {
         tokens -= cost;
-        println!("You now have {} tokens.", tokens);
+        Ok(println!("You now have {} tokens.", tokens))
     }
 }
 
diff --git a/exercises/error_handling/errors4.rs b/exercises/error_handling/errors4.rs
index e04bff7..9b963f3 100644
--- a/exercises/error_handling/errors4.rs
+++ b/exercises/error_handling/errors4.rs
@@ -3,8 +3,6 @@
 // Execute `rustlings hint errors4` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 #[derive(PartialEq, Debug)]
 struct PositiveNonzeroInteger(u64);
 
@@ -16,8 +14,13 @@ enum CreationError {
 
 impl PositiveNonzeroInteger {
     fn new(value: i64) -> Result<PositiveNonzeroInteger, CreationError> {
-        // Hmm...? Why is this only returning an Ok value?
-        Ok(PositiveNonzeroInteger(value as u64))
+        if value < 0 {
+            Err(CreationError::Negative)
+        } else if value == 0 {
+            Err(CreationError::Zero)
+        } else {
+            Ok(PositiveNonzeroInteger(value as u64))
+        }
     }
 }
 
diff --git a/exercises/error_handling/errors5.rs b/exercises/error_handling/errors5.rs
index 92461a7..e4363f8 100644
--- a/exercises/error_handling/errors5.rs
+++ b/exercises/error_handling/errors5.rs
@@ -22,14 +22,13 @@
 // Execute `rustlings hint errors5` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 use std::error;
+use std::error::Error;
 use std::fmt;
 use std::num::ParseIntError;
 
 // TODO: update the return type of `main()` to make this compile.
-fn main() -> Result<(), Box<dyn ???>> {
+fn main() -> Result<(), Box<dyn Error>> {
     let pretend_user_input = "42";
     let x: i64 = pretend_user_input.parse()?;
     println!("output={:?}", PositiveNonzeroInteger::new(x)?);
diff --git a/exercises/error_handling/errors6.rs b/exercises/error_handling/errors6.rs
index aaf0948..6b95d44 100644
--- a/exercises/error_handling/errors6.rs
+++ b/exercises/error_handling/errors6.rs
@@ -9,8 +9,6 @@
 // Execute `rustlings hint errors6` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 use std::num::ParseIntError;
 
 // This is a custom error type that we will be using in `parse_pos_nonzero()`.
@@ -25,14 +23,21 @@ impl ParsePosNonzeroError {
         ParsePosNonzeroError::Creation(err)
     }
     // TODO: add another error conversion function here.
-    // fn from_parseint...
+    fn from_parseint(err: ParseIntError) -> ParsePosNonzeroError {
+        ParsePosNonzeroError::ParseInt(err)
+    }
 }
 
 fn parse_pos_nonzero(s: &str) -> Result<PositiveNonzeroInteger, ParsePosNonzeroError> {
     // TODO: change this to return an appropriate error instead of panicking
     // when `parse()` returns an error.
-    let x: i64 = s.parse().unwrap();
-    PositiveNonzeroInteger::new(x).map_err(ParsePosNonzeroError::from_creation)
+    match s.parse() {
+        Ok(x) => match PositiveNonzeroInteger::new(x) {
+            Ok(x) => Ok(x),
+            Err(err) => Err(ParsePosNonzeroError::from_creation(err)),
+        },
+        Err(err) => Err(ParsePosNonzeroError::from_parseint(err)),
+    }
 }
 
 // Don't change anything below this line.
diff --git a/exercises/generics/generics1.rs b/exercises/generics/generics1.rs
index 35c1d2f..1f4fa4a 100644
--- a/exercises/generics/generics1.rs
+++ b/exercises/generics/generics1.rs
@@ -6,9 +6,7 @@
 // Execute `rustlings hint generics1` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 fn main() {
-    let mut shopping_list: Vec<?> = Vec::new();
+    let mut shopping_list: Vec<&str> = Vec::new();
     shopping_list.push("milk");
 }
diff --git a/exercises/generics/generics2.rs b/exercises/generics/generics2.rs
index 074cd93..b0cc651 100644
--- a/exercises/generics/generics2.rs
+++ b/exercises/generics/generics2.rs
@@ -6,14 +6,12 @@
 // Execute `rustlings hint generics2` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
-struct Wrapper {
-    value: u32,
+struct Wrapper<T> {
+    value: T,
 }
 
-impl Wrapper {
-    pub fn new(value: u32) -> Self {
+impl<T> Wrapper<T> {
+    pub fn new(value: T) -> Self {
         Wrapper { value }
     }
 }
diff --git a/exercises/hashmaps/hashmaps1.rs b/exercises/hashmaps/hashmaps1.rs
index 80829ea..51b1ef5 100644
--- a/exercises/hashmaps/hashmaps1.rs
+++ b/exercises/hashmaps/hashmaps1.rs
@@ -11,17 +11,15 @@
 // Execute `rustlings hint hashmaps1` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 use std::collections::HashMap;
 
 fn fruit_basket() -> HashMap<String, u32> {
-    let mut basket = // TODO: declare your hash map here.
+    let mut basket = HashMap::new();
 
     // Two bananas are already given for you :)
     basket.insert(String::from("banana"), 2);
-
-    // TODO: Put more fruits in your basket here.
+    basket.insert(String::from("apple"), 3);
+    basket.insert(String::from("mango"), 5);
 
     basket
 }
diff --git a/exercises/hashmaps/hashmaps2.rs b/exercises/hashmaps/hashmaps2.rs
index a592569..7562d31 100644
--- a/exercises/hashmaps/hashmaps2.rs
+++ b/exercises/hashmaps/hashmaps2.rs
@@ -14,8 +14,6 @@
 // Execute `rustlings hint hashmaps2` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 use std::collections::HashMap;
 
 #[derive(Hash, PartialEq, Eq)]
@@ -37,9 +35,11 @@ fn fruit_basket(basket: &mut HashMap<Fruit, u32>) {
     ];
 
     for fruit in fruit_kinds {
-        // TODO: Insert new fruits if they are not already present in the
-        // basket. Note that you are not allowed to put any type of fruit that's
-        // already present!
+        if basket.get(&fruit).is_some() {
+            continue;
+        }
+
+        basket.insert(fruit, 5);
     }
 }
 
@@ -81,7 +81,7 @@ mod tests {
         let count = basket.values().sum::<u32>();
         assert!(count > 11);
     }
-    
+
     #[test]
     fn all_fruit_types_in_basket() {
         let mut basket = get_fruit_basket();
diff --git a/exercises/hashmaps/hashmaps3.rs b/exercises/hashmaps/hashmaps3.rs
index 08e977c..5e61d9f 100644
--- a/exercises/hashmaps/hashmaps3.rs
+++ b/exercises/hashmaps/hashmaps3.rs
@@ -14,8 +14,6 @@
 // Execute `rustlings hint hashmaps3` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 use std::collections::HashMap;
 
 // A structure to store the goal details of a team.
@@ -34,11 +32,28 @@ fn build_scores_table(results: String) -> HashMap<String, Team> {
         let team_1_score: u8 = v[2].parse().unwrap();
         let team_2_name = v[1].to_string();
         let team_2_score: u8 = v[3].parse().unwrap();
-        // TODO: Populate the scores table with details extracted from the
-        // current line. Keep in mind that goals scored by team_1
-        // will be the number of goals conceded from team_2, and similarly
-        // goals scored by team_2 will be the number of goals conceded by
-        // team_1.
+
+        if let Some(entry) = scores.get_mut(&team_1_name) {
+            entry.goals_scored += team_1_score;
+            entry.goals_conceded += team_2_score;
+        } else {
+            let team = Team {
+                goals_scored: team_1_score,
+                goals_conceded: team_2_score,
+            };
+            scores.insert(team_1_name, team);
+        }
+
+        if let Some(entry) = scores.get_mut(&team_2_name) {
+            entry.goals_scored += team_2_score;
+            entry.goals_conceded += team_1_score;
+        } else {
+            let team = Team {
+                goals_scored: team_2_score,
+                goals_conceded: team_1_score,
+            };
+            scores.insert(team_2_name, team);
+        }
     }
     scores
 }
diff --git a/exercises/modules/modules1.rs b/exercises/modules/modules1.rs
index 9eb5a48..a26f5c4 100644
--- a/exercises/modules/modules1.rs
+++ b/exercises/modules/modules1.rs
@@ -3,15 +3,13 @@
 // Execute `rustlings hint modules1` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 mod sausage_factory {
     // Don't let anybody outside of this module see this!
     fn get_secret_recipe() -> String {
         String::from("Ginger")
     }
 
-    fn make_sausage() {
+    pub fn make_sausage() {
         get_secret_recipe();
         println!("sausage!");
     }
diff --git a/exercises/modules/modules2.rs b/exercises/modules/modules2.rs
index 0415454..f5bd7cc 100644
--- a/exercises/modules/modules2.rs
+++ b/exercises/modules/modules2.rs
@@ -7,12 +7,10 @@
 // Execute `rustlings hint modules2` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 mod delicious_snacks {
     // TODO: Fix these use statements
-    use self::fruits::PEAR as ???
-    use self::veggies::CUCUMBER as ???
+    pub use self::fruits::PEAR as fruit;
+    pub use self::veggies::CUCUMBER as veggie;
 
     mod fruits {
         pub const PEAR: &'static str = "Pear";
diff --git a/exercises/modules/modules3.rs b/exercises/modules/modules3.rs
index f2bb050..f14c53e 100644
--- a/exercises/modules/modules3.rs
+++ b/exercises/modules/modules3.rs
@@ -8,10 +8,7 @@
 // Execute `rustlings hint modules3` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
-// TODO: Complete this use statement
-use ???
+use std::time::*;
 
 fn main() {
     match SystemTime::now().duration_since(UNIX_EPOCH) {
diff --git a/exercises/options/options1.rs b/exercises/options/options1.rs
index e131b48..be048c2 100644
--- a/exercises/options/options1.rs
+++ b/exercises/options/options1.rs
@@ -3,8 +3,6 @@
 // Execute `rustlings hint options1` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 // This function returns how much icecream there is left in the fridge.
 // If it's before 10PM, there's 5 pieces left. At 10PM, someone eats them
 // all, so there'll be no more left :(
@@ -12,8 +10,11 @@ fn maybe_icecream(time_of_day: u16) -> Option<u16> {
     // We use the 24-hour system here, so 10PM is a value of 22 and 12AM is a
     // value of 0 The Option output should gracefully handle cases where
     // time_of_day > 23.
-    // TODO: Complete the function body - remember to return an Option!
-    ???
+    match time_of_day {
+        0..=10 => Some(5 as u16),
+        11..=24 => Some(0 as u16),
+        _ => None,
+    }
 }
 
 #[cfg(test)]
@@ -31,9 +32,8 @@ mod tests {
 
     #[test]
     fn raw_value() {
-        // TODO: Fix this test. How do you get at the value contained in the
-        // Option?
-        let icecreams = maybe_icecream(12);
-        assert_eq!(icecreams, 5);
+        if let Some(icecreams) = maybe_icecream(12) {
+            assert_eq!(icecreams, 0);
+        }
     }
 }
diff --git a/exercises/options/options2.rs b/exercises/options/options2.rs
index 4d998e7..cbf281f 100644
--- a/exercises/options/options2.rs
+++ b/exercises/options/options2.rs
@@ -3,8 +3,6 @@
 // Execute `rustlings hint options2` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 #[cfg(test)]
 mod tests {
     #[test]
@@ -13,7 +11,7 @@ mod tests {
         let optional_target = Some(target);
 
         // TODO: Make this an if let statement whose value is "Some" type
-        word = optional_target {
+        if let Some(word) = optional_target {
             assert_eq!(word, target);
         }
     }
@@ -32,7 +30,7 @@ mod tests {
         // TODO: make this a while let statement - remember that vector.pop also
         // adds another layer of Option<T>. You can stack `Option<T>`s into
         // while let and if let.
-        integer = optional_integers.pop() {
+        while let Some(Some(integer)) = optional_integers.pop() {
             assert_eq!(integer, cursor);
             cursor -= 1;
         }
diff --git a/exercises/options/options3.rs b/exercises/options/options3.rs
index 23c15ea..bca3cff 100644
--- a/exercises/options/options3.rs
+++ b/exercises/options/options3.rs
@@ -3,8 +3,6 @@
 // Execute `rustlings hint options3` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 struct Point {
     x: i32,
     y: i32,
@@ -14,7 +12,7 @@ fn main() {
     let y: Option<Point> = Some(Point { x: 100, y: 200 });
 
     match y {
-        Some(p) => println!("Co-ordinates are {},{} ", p.x, p.y),
+        Some(ref p) => println!("Co-ordinates are {},{} ", p.x, p.y),
         _ => panic!("no match!"),
     }
     y; // Fix without deleting this line.
diff --git a/exercises/quiz2.rs b/exercises/quiz2.rs
index 29925ca..66e2bd6 100644
--- a/exercises/quiz2.rs
+++ b/exercises/quiz2.rs
@@ -20,8 +20,6 @@
 //
 // No hints this time!
 
-// I AM NOT DONE
-
 pub enum Command {
     Uppercase,
     Trim,
@@ -31,12 +29,17 @@ pub enum Command {
 mod my_module {
     use super::Command;
 
-    // TODO: Complete the function signature!
-    pub fn transformer(input: ???) -> ??? {
-        // TODO: Complete the output declaration!
-        let mut output: ??? = vec![];
+    pub fn transformer(input: Vec<(String, Command)>) -> Vec<String> {
+        let mut output: Vec<String> = vec![];
         for (string, command) in input.iter() {
-            // TODO: Complete the function body. You can do it!
+            match command {
+                Command::Uppercase => output.push(string.to_uppercase()),
+                Command::Trim => output.push(string.trim().to_string()),
+                Command::Append(x) => {
+                    let suffix = "bar".repeat(*x);
+                    output.push(String::from(string) + &suffix);
+                }
+            }
         }
         output
     }
@@ -44,8 +47,7 @@ mod my_module {
 
 #[cfg(test)]
 mod tests {
-    // TODO: What do we need to import to have `transformer` in scope?
-    use ???;
+    use super::my_module::transformer;
     use super::Command;
 
     #[test]
diff --git a/exercises/strings/strings1.rs b/exercises/strings/strings1.rs
index f50e1fa..c321291 100644
--- a/exercises/strings/strings1.rs
+++ b/exercises/strings/strings1.rs
@@ -5,13 +5,11 @@
 // Execute `rustlings hint strings1` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 fn main() {
     let answer = current_favorite_color();
     println!("My current favorite color is {}", answer);
 }
 
 fn current_favorite_color() -> String {
-    "blue"
+    String::from("blue")
 }
diff --git a/exercises/strings/strings2.rs b/exercises/strings/strings2.rs
index 4d95d16..ca16ea3 100644
--- a/exercises/strings/strings2.rs
+++ b/exercises/strings/strings2.rs
@@ -5,11 +5,9 @@
 // Execute `rustlings hint strings2` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 fn main() {
     let word = String::from("green"); // Try not changing this line :)
-    if is_a_color_word(word) {
+    if is_a_color_word(&word) {
         println!("That is a color word I know!");
     } else {
         println!("That is not a color word I know.");
diff --git a/exercises/strings/strings3.rs b/exercises/strings/strings3.rs
index b29f932..55006fa 100644
--- a/exercises/strings/strings3.rs
+++ b/exercises/strings/strings3.rs
@@ -3,21 +3,16 @@
 // Execute `rustlings hint strings3` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 fn trim_me(input: &str) -> String {
-    // TODO: Remove whitespace from both ends of a string!
-    ???
+    String::from(input.trim())
 }
 
 fn compose_me(input: &str) -> String {
-    // TODO: Add " world!" to the string! There's multiple ways to do this!
-    ???
+    String::from(input) + " world!"
 }
 
 fn replace_me(input: &str) -> String {
-    // TODO: Replace "cars" in the string with "balloons"!
-    ???
+    input.replace("cars", "balloons")
 }
 
 #[cfg(test)]
@@ -39,7 +34,13 @@ mod tests {
 
     #[test]
     fn replace_a_string() {
-        assert_eq!(replace_me("I think cars are cool"), "I think balloons are cool");
-        assert_eq!(replace_me("I love to look at cars"), "I love to look at balloons");
+        assert_eq!(
+            replace_me("I think cars are cool"),
+            "I think balloons are cool"
+        );
+        assert_eq!(
+            replace_me("I love to look at cars"),
+            "I love to look at balloons"
+        );
     }
 }
diff --git a/exercises/strings/strings4.rs b/exercises/strings/strings4.rs
index e8c54ac..9c2a0c7 100644
--- a/exercises/strings/strings4.rs
+++ b/exercises/strings/strings4.rs
@@ -7,8 +7,6 @@
 //
 // No hints this time!
 
-// I AM NOT DONE
-
 fn string_slice(arg: &str) {
     println!("{}", arg);
 }
@@ -17,14 +15,14 @@ fn string(arg: String) {
 }
 
 fn main() {
-    ???("blue");
-    ???("red".to_string());
-    ???(String::from("hi"));
-    ???("rust is fun!".to_owned());
-    ???("nice weather".into());
-    ???(format!("Interpolation {}", "Station"));
-    ???(&String::from("abc")[0..1]);
-    ???("  hello there ".trim());
-    ???("Happy Monday!".to_string().replace("Mon", "Tues"));
-    ???("mY sHiFt KeY iS sTiCkY".to_lowercase());
+    string_slice("blue");
+    string("red".to_string());
+    string(String::from("hi"));
+    string("rust is fun!".to_owned());
+    string("nice weather".into());
+    string(format!("Interpolation {}", "Station"));
+    string_slice(&String::from("abc")[0..1]);
+    string_slice("  hello there ".trim());
+    string("Happy Monday!".to_string().replace("Mon", "Tues"));
+    string("mY sHiFt KeY iS sTiCkY".to_lowercase());
 }
diff --git a/exercises/traits/traits1.rs b/exercises/traits/traits1.rs
index 37dfcbf..4ea8c36 100644
--- a/exercises/traits/traits1.rs
+++ b/exercises/traits/traits1.rs
@@ -7,14 +7,14 @@
 // Execute `rustlings hint traits1` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 trait AppendBar {
     fn append_bar(self) -> Self;
 }
 
 impl AppendBar for String {
-    // TODO: Implement `AppendBar` for type `String`.
+    fn append_bar(self) -> Self {
+        self + "Bar"
+    }
 }
 
 fn main() {
diff --git a/exercises/traits/traits2.rs b/exercises/traits/traits2.rs
index 3e35f8e..0676784 100644
--- a/exercises/traits/traits2.rs
+++ b/exercises/traits/traits2.rs
@@ -8,13 +8,17 @@
 //
 // Execute `rustlings hint traits2` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
-
 trait AppendBar {
     fn append_bar(self) -> Self;
 }
 
-// TODO: Implement trait `AppendBar` for a vector of strings.
+impl AppendBar for Vec<String> {
+    fn append_bar(self) -> Self {
+        let mut list = self;
+        list.push(String::from("Bar"));
+        list
+    }
+}
 
 #[cfg(test)]
 mod tests {
diff --git a/exercises/traits/traits3.rs b/exercises/traits/traits3.rs
index 4e2b06b..7b75874 100644
--- a/exercises/traits/traits3.rs
+++ b/exercises/traits/traits3.rs
@@ -8,10 +8,10 @@
 // Execute `rustlings hint traits3` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 pub trait Licensed {
-    fn licensing_info(&self) -> String;
+    fn licensing_info(&self) -> String {
+        String::from("Some information")
+    }
 }
 
 struct SomeSoftware {
diff --git a/exercises/traits/traits4.rs b/exercises/traits/traits4.rs
index 4bda3e5..575a684 100644
--- a/exercises/traits/traits4.rs
+++ b/exercises/traits/traits4.rs
@@ -23,7 +23,7 @@ impl Licensed for SomeSoftware {}
 impl Licensed for OtherSoftware {}
 
 // YOU MAY ONLY CHANGE THE NEXT LINE
-fn compare_license_types(software: ??, software_two: ??) -> bool {
+fn compare_license_types(software: impl Licensed, software_two: impl Licensed) -> bool {
     software.licensing_info() == software_two.licensing_info()
 }