Answer
$\dfrac{y^3}{x}$
Work Step by Step
RECALL:
$a^{-m} = \dfrac{1}{a^m}, m\gt0$
Use the rule above to obtain:
$\dfrac{x^{-1}}{y^{-3}}=\dfrac{\frac{1}{x^1}}{\frac{1}{y^3}}$
Use the rule $\frac{a}{b} \div \frac{c}{d}=\frac{a}{b} \times \frac{d}{c}$ to obtain:
$=\dfrac{1}{x} \cdot \dfrac{y^3}{1}
\\=\dfrac{y^3}{x}$
