Chapter 5 - Section 5.2 - More Work with Exponents and Scientific Notation - Exercise Set - Page 268: 21

$\dfrac{64}{27}$

\text{ Using laws of exponents, the given expression simpifies to }\\ \begin{align*} & \left( \dfrac{3}{4} \right)^{-3} \\\\&= \dfrac{3^{-3}}{4^{-3}} \\\\&= \dfrac{4^{3}}{3^{3}} \\\\&= \dfrac{64}{27} .\end{align*}