#### Answer

$6\sqrt 2$

#### Work Step by Step

We break the square root into its factors, and then we simplify the factors that are perfect squares:
$\sqrt 6\times\sqrt {12}$
=$\sqrt {6\times12}$
=$\sqrt {72}$
=$\sqrt {2\times36}$
=$\sqrt 2\times\sqrt {36}$
=$\sqrt 2\times6$
=$6\sqrt 2$