I had a lot of trouble getting Exercise 1 to work at first. Ultimately, it turned out I had forgotten that the position of a given character was counted from 0, not 1.

Exercise 3 was a challenge because I kept trying to use letter in too many places. I had to remind myself to be methodical here, and I went line by line to identify the issue. An excellent reminder to be patient and be careful of details.

Exercise 4 worked immediately.

Exercise 5 was likewise straightforward. In the end, the challenge with Chapter 6 was not sticking too close to the text. I think I was too stuck on imitating the book when I was trying to complete Exercise 3. Straying from it, and finding what worked within the context of the exercise, was a much more successful strategy.