Algebra

$18\sqrt{8}-8\sqrt{2}=\sqrt{n}$

$1568=n$

Simple 

-Vinculum

$$18\sqrt{8} - 8\sqrt{2} = \sqrt{n}$$

we need to solve the left hand side then square it because there is a sqrt on the right side, and that gives us

$$1568, so \ n=1568$$