A Word on the Challenges

There's an easy way to do the exercises: Read the question, look up the answer, and nod because it sounds plausible. This may lead you to my insights.

Then there's a harder but far better way to do the exercises: Read the question, solve the problem, and only then look up the answer. This has a much better chance of leading you to your own insights.

Particularly for the code you're asked to modify, hands-on practice will help you learn more. Refactoring is a skill that requires practice.

Good luck!