#### Answer

positive and negative 15

#### Work Step by Step

The problem is $b^{2} - 225 =0$ so first we must isolate the variable. To do this, we move 225 to the other side of the equation. Then, we get $b^{2} = 225$ and we put a square root over both $b^{2}$ and $225$ to get b= positive and negative 15.