Chapter 5 - Section 5.2 - More Work with Exponents and Scientific Notation - Exercise Set - Page 268: 68

$\dfrac{8y^{-a+b}}{x^{3a+3b}}$

Using laws of exponents, the given expression simplifies to \begin{align*} & \dfrac{16x^{-5-3a}y^{-2a-b}}{2x^{-5+3b}y^{-2b-a}} \\\\&= (16\div2)x^{-5-3a-(-5+3b)}y^{-2a-b-(-2b-a)} \\\\&= 8x^{-5-3a+5-3b}y^{-2a-b+2b+a} \\\\&= 8x^{-3a-3b}y^{-a+b} \\\\&= \dfrac{8y^{-a+b}}{x^{3a+3b}} .\end{align*}