Answer
$6|a|$
Work Step by Step
Using $\sqrt{x^2}=|x|$, the given expression, $
\sqrt[4]{(6a)^4}
,$ simplifies to
\begin{array}{l}
|6a|
\\\\=
6|a|
.\end{array}
We put the variable in absolute value bars since it is being raised to an odd power.