#### Answer

$\dfrac{x^{2}+5x}{8}\cdot\dfrac{9}{3x+15}=\dfrac{3x}{8}$

#### Work Step by Step

$\dfrac{x^{2}+5x}{8}\cdot\dfrac{9}{3x+15}$
Take out common factor $x$ from the numerator of the first fraction and common factor $3$ from the denominator of the second fraction:
$\dfrac{x^{2}+5x}{8}\cdot\dfrac{9}{3x+15}=\dfrac{x(x+5)}{8}\cdot\dfrac{9}{3(x+5)}=...$
Evaluate the product of the two rational expressions and then simplify by removing repeated factors in the numerator and the denominator:
$...=\dfrac{9x(x+5)}{24(x+5)}=\dfrac{9x}{24}=\dfrac{3x}{8}$