#### Answer

$-\dfrac{5a^{2}b}{30a^{2}b^{2}}\cdot b^{3}=-\dfrac{b^{2}}{6}$

#### Work Step by Step

$-\dfrac{5a^{2}b}{30a^{2}b^{2}}\cdot b^{3}$
Multiply both expressions and simplify by removing repeated factors in the numerator and the denominator:
$-\dfrac{5a^{2}b}{30a^{2}b^{2}}\cdot b^{3}=-\dfrac{5a^{2}b^{4}}{30a^{2}b^{2}}=-\dfrac{5b^{2}}{30}=-\dfrac{b^{2}}{6}$