#### Answer

$-18 \sqrt{5}$

#### Work Step by Step

In order to simplify a radical, we consider the factors of the number inside of the radical. If any of these factors are perfect squares, meaning that their square root is a whole number, then we can simplify the radical. We know that 5 and 9 are factors of 45. We know that 9 is a perfect square, so we simplify:
$-6 \sqrt{9} \sqrt{5}=-18 \sqrt{5}$