Exercise 8 - explaining the difference between a comma inside and outside of the repetition braces. #61

This book is great! I just completed exercise 8, and I had some trouble with understanding how I actually solved it - I knew it had something to do with putting separators in the correct place, so I looked it up and found this SO answer: https://stackoverflow.com/a/66432373/16887886
I suggest incorporating that information into this exercise (#8)? Technically I guess this information really belongs in exercise 6, but I think it may be more useful to explain this with an exercise that requires both kinds of separator usage.