#### Answer

$-4i\sqrt5$

#### Work Step by Step

Factor the radicand so that one factor is a perfect square then simplify to obtain:
$=-\sqrt{16(-5)}
\\=-\sqrt{4^2(-5)}
\\=-4\sqrt{-4}$
Factor out $-1$ in the radicand to obtain:
$=-4\sqrt{-1(5)}$
Since $\sqrt{-1} = i$, bring out the square root of $-1$, which is $i$, to obtain:
$=-4i\sqrt5$