#### Answer

$= \frac{(r-3)}{(r+5)}$

#### Work Step by Step

$\frac{r^{2}-36}{r^{2}-11r+30} \div \frac{r^{2}+11r+30}{r^{2}-8r+15}$
$= \frac{r^{2}-36}{r^{2}-11r+30} \times \frac{r^{2}-8r+15}{r^{2}+11r+30}$
$= \frac{(r-6)(r+6)}{(r-6)(r-5)} \times \frac{(r-3)(r-5)}{(r+6)(r+5)}$
$= \frac{(r+6)}{(r-5)} \times \frac{(r-3)(r-5)}{(r+6)(r+5)}$
$= \frac{(r+6)}{1} \times \frac{(r-3)}{(r+6)(r+5)}$
$= \frac{1}{1} \times \frac{(r-3)}{(r+5)}$
$= 1\times \frac{(r-3)}{(r+5)}$
$= \frac{(r-3)}{(r+5)}$