#### Answer

$\color{blue}{6a\sqrt{a}}$

#### Work Step by Step

Factor the radicand so that at least one factor is a perfect square:
$=\sqrt{(36a^2)(a)}
\\=\sqrt{(6a)^2(a)}$
Bring out the square root of the perfect square factor to obtain:
$=\color{blue}{6a\sqrt{a}}$