Equation for volume of a square is V=BH or V=LWH
if 2 inches are cut from each corner it decreases the size from 10 by 10 to 6 by 6
the 2 inches that were cut of now represent the height
so...
L=6
W=6
H=2
sub this into the formula to get L=6x6x2 which equals to 72 inches squared