1/4 * 6.16^2 - 4 * 1.04^2
=1/4*6.16*6.16- 4 * 1.04*1.04
=(6.16/2)^2- (1.04*2)^2
=3.08^2-2.08^2
=(3.08+2.08)*(3.08-2.08)
=5.16*1
=5.16