#### Answer

$\sqrt[3] 36xy$

#### Work Step by Step

The product rule for radicals tells us that $\sqrt[n] a\times\sqrt[n] b=\sqrt[n] ab$ (when $\sqrt[n] a$ and $\sqrt[n] b$ are real numbers and $n$ is a natural number). That is, the product of two nth roots is the nth root of the product.
Therefore, $\sqrt[3] 9x\times\sqrt[3] 4y=\sqrt[3] (9x\times 4y)=\sqrt[3] (9\times4\times x\times y)=\sqrt[3] 36xy$.