#### Answer

$4-2i\sqrt{15}$

#### Work Step by Step

Using $i=\sqrt{-1}$ and the properties of radicals, the given expression, $
4-\sqrt{-60}
,$ is equivalent to
\begin{array}{l}\require{cancel}
4-\sqrt{60}\cdot\sqrt{-1}
\\\\=
4-\sqrt{4\cdot15}\cdot i
\\\\=
4-\sqrt{(2)^2\cdot15}\cdot i
\\\\=
4-2i\sqrt{15}
.\end{array}