Answer
$3$
Work Step by Step
Using $a^{m/n}=\sqrt[n]{a^m}=(\sqrt[n]{a})^m$, the given expression, $
81^{1/4}
,$ is equivalent to
\begin{array}{l}\require{cancel}
\sqrt[4]{81^1}
\\\\=
\sqrt[4]{81}
\\\\=
\sqrt[4]{(3)^4}
\\\\=
3
.\end{array}