diff --git a/package.json b/package.json
index 1263eee..af25104 100644
--- a/package.json
+++ b/package.json
@@ -63,4 +63,4 @@
     "express": "^4.18.1",
     "zod": "^3.17.10"
   }
-}
+}
\ No newline at end of file
diff --git a/src/01-number.problem.ts b/src/01-number.problem.ts
index 0f6286e..5f21a88 100644
--- a/src/01-number.problem.ts
+++ b/src/01-number.problem.ts
@@ -1,6 +1,6 @@
 import { expect, it } from "vitest";
 
-export const addTwoNumbers = (a, b) => {
+export const addTwoNumbers = (a: number, b: number) => {
   return a + b;
 };
 
diff --git a/src/02-object-param.problem.ts b/src/02-object-param.problem.ts
index 8c33176..4b7248c 100644
--- a/src/02-object-param.problem.ts
+++ b/src/02-object-param.problem.ts
@@ -1,6 +1,6 @@
 import { expect, it } from "vitest";
 
-export const addTwoNumbers = (params) => {
+export const addTwoNumbers = (params: { first: number; second: number }) => {
   return params.first + params.second;
 };
 
diff --git a/src/03-optional-properties.problem.ts b/src/03-optional-properties.problem.ts
index 9ee58fc..a35619d 100644
--- a/src/03-optional-properties.problem.ts
+++ b/src/03-optional-properties.problem.ts
@@ -1,6 +1,6 @@
 import { expect, it } from "vitest";
 
-export const getName = (params: { first: string; last: string }) => {
+export const getName = (params: { first: string; last?: string }) => {
   if (params.last) {
     return `${params.first} ${params.last}`;
   }
diff --git a/src/04-optional-params.problem.ts b/src/04-optional-params.problem.ts
index 023bb99..3c12b9f 100644
--- a/src/04-optional-params.problem.ts
+++ b/src/04-optional-params.problem.ts
@@ -1,6 +1,6 @@
 import { expect, it } from "vitest";
 
-export const getName = (first: string, last: string) => {
+export const getName = (first: string, last?: string) => {
   if (last) {
     return `${first} ${last}`;
   }
diff --git a/src/05-assigning-types-to-variables.problem.ts b/src/05-assigning-types-to-variables.problem.ts
index 50de898..13e071b 100644
--- a/src/05-assigning-types-to-variables.problem.ts
+++ b/src/05-assigning-types-to-variables.problem.ts
@@ -11,7 +11,12 @@ interface User {
  * How do we ensure that defaultUser is of type User
  * at THIS LINE - not further down in the code?
  */
-const defaultUser = {};
+const defaultUser: User = {
+  id: 1,
+  firstName: "Matt",
+  lastName: "Pocock",
+  isAdmin: false,
+};
 
 const getUserId = (user: User) => {
   return user.id;
diff --git a/src/06-unions.problem.ts b/src/06-unions.problem.ts
index 55420fd..c441e65 100644
--- a/src/06-unions.problem.ts
+++ b/src/06-unions.problem.ts
@@ -8,7 +8,7 @@ interface User {
    * - 'user'
    * - 'super-admin'
    */
-  role: string;
+  role: "admin" | "user" | "super-admin";
 }
 
 export const defaultUser: User = {
diff --git a/src/07-arrays.problem.ts b/src/07-arrays.problem.ts
index c18909c..dda09a2 100644
--- a/src/07-arrays.problem.ts
+++ b/src/07-arrays.problem.ts
@@ -3,7 +3,7 @@ interface User {
   firstName: string;
   lastName: string;
   role: "admin" | "user" | "super-admin";
-  posts: Post;
+  posts: Post[];
 }
 
 interface Post {
diff --git a/src/08-function-return-type-annotations.problem.ts b/src/08-function-return-type-annotations.problem.ts
index af1e721..81cb5e7 100644
--- a/src/08-function-return-type-annotations.problem.ts
+++ b/src/08-function-return-type-annotations.problem.ts
@@ -17,8 +17,19 @@ interface Post {
  * How do we ensure that makeUser ALWAYS
  * returns a user?
  */
-const makeUser = () => {
-  return {};
+const makeUser = (): User => {
+  return {
+    id: 1,
+    firstName: "John",
+    lastName: "Doe",
+    role: "user",
+    posts: [
+      {
+        id: 1,
+        title: "How I eat so much cheese",
+      },
+    ],
+  };
 };
 
 it("Should return a valid user", () => {
diff --git a/src/09-promises.problem.ts b/src/09-promises.problem.ts
index cc5781b..851d1e0 100644
--- a/src/09-promises.problem.ts
+++ b/src/09-promises.problem.ts
@@ -9,7 +9,7 @@ interface LukeSkywalker {
   gender: string;
 }
 
-export const fetchLukeSkywalker = async (): LukeSkywalker => {
+export const fetchLukeSkywalker = async (): Promise<LukeSkywalker> => {
   const data = await fetch("https://swapi.py4e.com/api/people/1").then(
     (res) => {
       return res.json();
diff --git a/src/10-set.problem.ts b/src/10-set.problem.ts
index 0f318a4..0bd251c 100644
--- a/src/10-set.problem.ts
+++ b/src/10-set.problem.ts
@@ -1,7 +1,7 @@
 import { expect, it } from "vitest";
 import { Equal, Expect } from "./helpers/type-utils";
 
-const guitarists = new Set();
+const guitarists = new Set<string>();
 
 guitarists.add("Jimi Hendrix");
 guitarists.add("Eric Clapton");
diff --git a/src/11-record.problem.ts b/src/11-record.problem.ts
index 1cc7445..d913044 100644
--- a/src/11-record.problem.ts
+++ b/src/11-record.problem.ts
@@ -1,7 +1,7 @@
 import { expect, it } from "vitest";
 
 const createCache = () => {
-  const cache = {};
+  const cache:Record<string, string> = { };
 
   const add = (id: string, value: string) => {
     cache[id] = value;
diff --git a/src/12-typeof-narrowing.problem.ts b/src/12-typeof-narrowing.problem.ts
index 7811011..2069b4d 100644
--- a/src/12-typeof-narrowing.problem.ts
+++ b/src/12-typeof-narrowing.problem.ts
@@ -1,6 +1,11 @@
 import { expect, it } from "vitest";
 
-const coerceAmount = (amount: number | { amount: number }) => {};
+const coerceAmount = (amount: number | { amount: number }) => {
+  if (typeof amount === "number") {
+    return amount;
+  }
+  return amount.amount; 
+};
 
 it("Should return the amount when passed an object", () => {
   expect(coerceAmount({ amount: 20 })).toEqual(20);
diff --git a/src/13-catch-blocks.problem.ts b/src/13-catch-blocks.problem.ts
index 246d129..c47d936 100644
--- a/src/13-catch-blocks.problem.ts
+++ b/src/13-catch-blocks.problem.ts
@@ -6,7 +6,9 @@ const tryCatchDemo = (state: "fail" | "succeed") => {
       throw new Error("Failure!");
     }
   } catch (e) {
-    return e.message;
+    if (e instanceof Error) {
+      return e.message;
+    }
   }
 };
 
diff --git a/src/14-extends.problem.ts b/src/14-extends.problem.ts
index e468905..70fea5f 100644
--- a/src/14-extends.problem.ts
+++ b/src/14-extends.problem.ts
@@ -5,21 +5,20 @@ import { Equal, Expect } from "./helpers/type-utils";
  * interfaces. Can you find a way to refactor this to
  * make it more DRY?
  */
-
-interface User {
+interface Base {
   id: string;
+}
+interface User extends Base {
   firstName: string;
   lastName: string;
 }
 
-interface Post {
-  id: string;
+interface Post extends Base {
   title: string;
   body: string;
 }
 
-interface Comment {
-  id: string;
+interface Comment extends Base {
   comment: string;
 }
 
diff --git a/src/15-intersection.problem.ts b/src/15-intersection.problem.ts
index a6e5bc7..9569caa 100644
--- a/src/15-intersection.problem.ts
+++ b/src/15-intersection.problem.ts
@@ -14,7 +14,7 @@ interface Post {
  * How do we type this return statement so it's both
  * User AND { posts: Post[] }
  */
-export const getDefaultUserAndPosts = (): unknown => {
+export const getDefaultUserAndPosts = (): User & { posts: Post[] } => {
   return {
     id: "1",
     firstName: "Matt",
diff --git a/src/16-omit-and-pick.problem.ts b/src/16-omit-and-pick.problem.ts
index 8d75c8b..99e18ff 100644
--- a/src/16-omit-and-pick.problem.ts
+++ b/src/16-omit-and-pick.problem.ts
@@ -11,6 +11,6 @@ interface User {
  * firstName and lastName properties of User?
  */
 
-type MyType = unknown;
+type MyType = Pick<User, "firstName" | "lastName">;
 
 type tests = [Expect<Equal<MyType, { firstName: string; lastName: string }>>];
diff --git a/src/17-function-types.problem.ts b/src/17-function-types.problem.ts
index a228d9e..12e6a41 100644
--- a/src/17-function-types.problem.ts
+++ b/src/17-function-types.problem.ts
@@ -3,7 +3,7 @@ import { Equal, Expect } from "./helpers/type-utils";
 /**
  * How do we type onFocusChange?
  */
-const addListener = (onFocusChange: unknown) => {
+const addListener = (onFocusChange: (isFocused: boolean) => void) => {
   window.addEventListener("focus", () => {
     onFocusChange(true);
   });
diff --git a/src/18-function-types-with-promises.problem.ts b/src/18-function-types-with-promises.problem.ts
index 086ad34..5642baf 100644
--- a/src/18-function-types-with-promises.problem.ts
+++ b/src/18-function-types-with-promises.problem.ts
@@ -7,8 +7,8 @@ interface User {
 }
 
 const createThenGetUser = async (
-  createUser: unknown,
-  getUser: unknown,
+  createUser: () => Promise<string>,
+  getUser: (id: string) => Promise<User>,
 ): Promise<User> => {
   const userId: string = await createUser();