#### Answer

$9\sqrt{3}$

#### Work Step by Step

Simplifying each term and then combining like terms, the given expression, $
4\sqrt{27}-3\sqrt{3}
,$ is equivalent to
\begin{array}{l}\require{cancel}
4\sqrt{9\cdot3}-3\sqrt{3}
\\\\=
4\sqrt{(3)^2\cdot3}-3\sqrt{3}
\\\\=
4\cdot3\sqrt{3}-3\sqrt{3}
\\\\=
12\sqrt{3}-3\sqrt{3}
\\\\=
9\sqrt{3}
.\end{array}