Answer
$\frac{3}{2}$
Work Step by Step
We know that $\sqrt[4] \frac{81}{16}=\frac{3}{2}$, because $(\frac{3}{2})^{4}=\frac{3}{2}\times\frac{3}{2}\times\frac{3}{2}\times\frac{3}{2}=\frac{3\times3\times3\times3}{2\times2\times2\times2}=\frac{81}{16}$.