Answer
$-20m^{5}n^{9}$
Work Step by Step
We are given the expression $5m^{3}n^{4}(-4m^{2}n^{5})$. We can group like terms and then simplify.
$5\times-4\times m^{3} \times m^{2}\times n^{4}\times n^{5}$
Next, we can use the product rule for exponents to multiply the exponents.
$-20\times m^{3+2}\times n^{4+5}=-20m^{5}n^{9}$