REally its so simple its difficult

--> Without a calculator simplify $\displaystyle \sqrt18 . \sqrt24 $

I get as far as $\displaystyle \sqrt3\sqrt6 . \sqrt4\sqrt6 $

$\displaystyle \sqrt3\sqrt6 . 2\sqrt6 $

the book says the ans is $\displaystyle 24\sqrt3 $

But i have no clue how to achive that answer