There are two things to be careful with in this problem.
First, each term in the second expression is being subtracted, so we must "distribute" the subtraction sign to each term when removing the parentheses.
Notice also that when we distribute the subtraction to another subtraction, it becomes addition.
The second thing we need to be cautious with is the last term, b. Even though it doesn't show a coefficient, it is the same as 1b.
Our simplified expression is: