Answer
$-\frac{\sqrt[4]{m}}{n}$
Work Step by Step
Apply the rule: $\sqrt[n]{\frac{a}{b}}=\frac{\sqrt[n]{a}}{\sqrt[n]{b}}$
$-\sqrt[4]{\frac{m}{n^4}}=-\frac{\sqrt[4]{m}}{\sqrt[4]{n^4}}$
Evaluate and simplify.
$-\sqrt[4]{\frac{m}{n^4}}=-\frac{\sqrt[4]{m}}{n}$