#### Answer

$i\sqrt{2}$

#### Work Step by Step

Divide the inside of each radical with one radical over both of them.
$\sqrt{\frac{-54}{27}}$
Simplify.
$\sqrt{\frac{-54}{27}}=\sqrt{-2}$
Pull the negative inside the radical into an imaginary number outside of the radical.
$i\sqrt{2}$