Chapter 5 - Section 5.2 - More Work with Exponents and Scientific Notation - Exercise Set - Page 268: 33

$\dfrac{1}{x^{20}y^{15}}$

Using laws of exponents, the given expression simplifies to \begin{align*} & \left( \dfrac{x^4}{y^{-3}} \right)^{-5} \\\\&= \dfrac{x^{4(-5)}}{y^{-3(-5)}} \\\\&= \dfrac{x^{-20}}{y^{15}} \\\\&= \dfrac{1}{x^{20}y^{15}} .\end{align*}