You started to make a u-substitution, but you should have instead of . If you solve for x in terms of u, you get x=u-1. So you have everything you need to make the substitution:

It's a little easier to see how to proceed now.

The book doesn't make the substitution. It just uses x+1 "as is" instead of u. But the steps are the same.

Hope this helps,

Hollywood