corrections to chapter 2

[KatherineCox]

I think I found a few mistakes in the key.

I'm working through the book myself (self-study), so double check my fixes.

For future reference, would you rather have each correction be a separate PR or is a few at a time okay?

[spamegg1]

Thanks for the fixes! ❤️
If they are a few small fixes, it's OK to have them in one PR.
If it changes a solution's logic, then it would be better as a separate PR.

[spamegg1]

I checked them all, thanks again! ❤️