Answer
$$\left(b-3\right)^2\left(b+3\right)$$
Work Step by Step
Factoring the expression completely, we find:
$$ -9\left(b-3\right)+b^2\left(b-3\right) \\ \left(b-3\right)\left(b^2-9\right) \\ \text { Recognize the difference of squares } \\ \left(b-3\right)\left(b+3\right)\left(b-3\right) \\ \left(b-3\right)^2\left(b+3\right)$$
