Answer
$9\sqrt{2}$.
Work Step by Step
The given expression is
$=5\sqrt{18}-3\sqrt{8}$
Factor radicands as a perfect square.
$=5\sqrt{3^2\cdot 2}-3\sqrt{2^2\cdot 2}$
Simplify.
$=5\cdot 3\sqrt{2}-3\cdot 2\sqrt{2}$
$=15\sqrt{2}-6\sqrt{2}$
Use the distributive property.
$=(15-6)\sqrt{2}$
Simplify.
$=9\sqrt{2}$.
