Answer
$=-\frac{216}{y^{3}}$
Work Step by Step
When a quotient is raised to a power, raise both the numerator and the denominator to that power:
$$(-\frac{6}{y})^{3}$$
$$=\frac{(-6)^{3}}{y^{3}}$$
$$=\frac{-216}{y^{3}}$$
$$=-\frac{216}{y^{3}}$$