#### Answer

$15+9\sqrt2$

#### Work Step by Step

$(\sqrt{3}+\sqrt6)(\sqrt{3}+2\sqrt6)$
Use the FOIL method to multiply the binomial.
Multiply the First terms, the Outside terms, the Inside terms, and the Last terms.
$(\sqrt{3}\times\sqrt{3})+(\sqrt3\times2\sqrt{6})+(\sqrt3\times\sqrt{6})+(\sqrt6\times2\sqrt6)$
Simplify.
$3+2\sqrt{18}+\sqrt{18}+12$
Combine like terms/like radicals.
$15+3\sqrt{18}$
Simplify
$15+3\sqrt{9\times2}$
$15+3(3)(\sqrt2)$
$15+9\sqrt2$