Hello!You have to multiply 1 1/4 by 30 because each math book is 1 1/4 in. thick, and 30 books is 1 1/4 by 30. First change 30 and 1 1/4 to an improper fraction.

The answer for your question is b
The restrictions are what the denominator can not be. The denominator cannot be zero. So if the denominator has x+1 in it. If you put -1 in place of x. You would get zero. -1 is a restriction