Answer
$\sqrt[3]{3x}$
Work Step by Step
Recall the property (pg. 369):
$\dfrac{\sqrt[n]{a}}{\sqrt[n]{b}}=\sqrt[n]{\dfrac{a}{b}}$ (if $\sqrt[n]{a}$ and $\sqrt[n]{b}$ are real numbers and $b\ne 0$)
We use this property to simplify the given expression:
$=\dfrac{\sqrt[3]{15x^2}}{\sqrt[3]{5x}}$
$=\sqrt[3]{\dfrac{15x^2}{5x}}$
$=\sqrt[3]{3x}$