PWN 4th Edition –> Page 100, Question 2

HI!
I have a quick question on one of the practice questions. There was an explanation offered, but I’m still confused 🙁

This is for PWN 4th Edition –> Page 100, Question 2
f(x-1) = X +1 for all values of x, which of the following is equal to f(x+1)?
The explanation in the back of the book is a bit unclear to me and I really need another way to look at this problem Any help is appreciated, thanks in advance!