Answer
$-49xy^{2}$
Work Step by Step
We are given the expression $(-7xy)(7y)$.
$(-7xy)\times(7y)=(-7\times7)\times(x)\times(y\times y)$
We can use the product rule to simplify the third term, which holds that $a^{m}\times a^{n}=a^{m+n}$.
Therefore, $(-7\times7)\times(x)\times(y\times y)=-49\times x\times y^{1+1}=-49xy^{2}$