Answer
$-72m^{3}n^{8}$
Work Step by Step
Based on the product rule for exponents, we know that $a^{m}\times a^{n}=a^{m+n}$ (where $m$ and $n$ are positive integers and $a$ is a real number).
Therefore, $(-8mn^{6})(9m^{2}n^{2})=-8\times9\times m^{1+2}\times n^{6+2}=-72\times m^{3}\times n^{8}=-72m^{3}n^{8}$.