If 36 sqrt2 - 24 sqrt2 = sqrtn, what is n?

N = 288

First, both 36 sqrt 2 and 24 sqrt 2 have the common sqrt 2, which means you can directly subtract them.

36 sqrt 2 - 24 sqrt 2 = 12 sqrt 2
12 is outside of the square root means it was a perfect square, thus 12*12 = 144.

There's still a 2 left in the sqrt, and 144 * 2 = 288.