Answer
$26m^{9}n^{7}$
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, $(-2mn^{6})(-13m^{8}n)=-2\times-13\times m^{1+8}\times n^{6+1}=26m^{9}n^{7}$.