Answer
$\displaystyle \frac{x}{ab}$
Work Step by Step
First. in the denominator of the radicand, $a^{4}b^{4}=(ab)^{4}$,
so the radicand equals $\displaystyle \frac{x^{4}}{(ab)^{4}}$ ,
which, after applying the rule: $(\displaystyle \frac{a}{b})^{n}=\frac{a^{n}}{b^{n}}$
equals $(\displaystyle \frac{x}{ab})^{4}$, we have
$\sqrt[4]{ (\displaystyle \frac{x}{ab})^{4}}$
Now, for even n, $\sqrt[n]{x^{n}}=|x|$, so
$\sqrt[4]{ (\displaystyle \frac{x}{ab})^{4}}=|\frac{x}{ab}|$
We are told that x, a and b are positive, so we remove the absolute bracket
$=\displaystyle \frac{x}{ab}$
