#### Answer

$6i$

#### Work Step by Step

Using the properties of radicals and that $i=\sqrt{-1}$, then the given expression, $
\sqrt{-36}
,$ is equivalent to
\begin{array}{l}\require{cancel}
\sqrt{-1}\cdot\sqrt{36}
\\\\=
i\cdot\sqrt{(6)^2}
\\\\=
i\cdot6
\\\\=
6i
.\end{array}