Answer
$\color{blue}{\dfrac{y^2}{2}}
$
Work Step by Step
Use the rule $\frac{a}{b} \div \frac{c}{d} = \frac{a}{b} \cdot \frac{d}{c}$ to obtain:
$=\dfrac{y^3}{8} \cdot \dfrac{4}{y}$
Cancel the common factors first before performing the actual multiplication to obtain:
$\require{cancel}
=\dfrac{\cancel{y^3}y^2}{\cancel{8}2} \cdot \dfrac{\cancel{4}}{\cancel{y}}
\\=\dfrac{y^2}{2} \cdot \dfrac{1}{1}
\\=\color{blue}{\dfrac{y^2}{2}}
$
