Chapter 5 - Section 5.2 - More Work with Exponents and Scientific Notation - Exercise Set - Page 268: 46

$\dfrac{2}{y^6}$

Using laws of exponents, the given expression simplifies to \begin{align*} & \dfrac{2(y^3)^{-3}}{y^{-3}} \\\\&= \dfrac{2y^{3(-3)}}{y^{-3}} \\\\&= \dfrac{2y^{-9}}{y^{-3}} \\\\&= 2y^{-9-(-3)} \\&= 2y^{-6} \\\\&= \dfrac{2}{y^6} .\end{align*}