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.
