Chapter 5 - Exponents and Polynomials - 5.6 - Integral Exponents and Scientific Notation - Problem Set 5.6 - Page 224: 78

$\dfrac{x^{3}}{y^{4}}$

Using the laws of exponents, the given expression, $ \left( \dfrac{x^{-3}}{y^{-4}} \right)^{-1} ,$ is equivalent to \begin{array}{l}\require{cancel} \dfrac{x^{-3(-1)}}{y^{-4(-1)}} \\\\= \dfrac{x^{3}}{y^{4}} .\end{array}