Begin by rewriting the expression as $\left(\left(\frac{1}{81}\right)^{-1}\right)^{\frac{1}{4}}$.

Since$\left(\frac{1}{81}\right)^{-1}=81$, the expression can be rewritten as $(81)^\frac{1}{4}$.

The negative exponents mean you will be finding the reciprocals of the factors.

There are several ways to simplify this expression. Here is one:

$\frac{1}{(2x)^{2}}(16)^{\frac{1}{2}}(x^{2})^{\frac{1}{2}}(y)^{\frac{1}{2}}$

$\frac{1}{4x^2}(4)(x)(y)^{\frac{1}{2}}$

$\frac{(y)^{\frac{1}{2}}}{x}$  or $\frac{\sqrt{y}}{x}$