Chapter 5 - Section 5.2 - More Work with Exponents and Scientific Notation - Exercise Set - Page 268: 43

$\dfrac{x^{4}}{16}$

Using laws of exponents, the given expression simplifies to \begin{align*} & \left( \dfrac{3x^5}{6x^{4}} \right)^4 \\\\&= \left( \dfrac{x^{5-4}}{2} \right)^4 \\\\&= \left( \dfrac{x^{}}{2} \right)^4 \\\\&= \dfrac{x^{4}}{2^4} \\\\&= \dfrac{x^{4}}{16} .\end{align*}