B = (x+5) (5x-1)+(5x-1)(2x+15)
C = (2x+5)(6x+1)-(6x+1)(-x+5)
D = (4-x)² -(5x-3)(4-x)
E = x² - 18x +81
F = 16x² - 9
G = x² + 10x + 25
H = x ² -25 + (x+5) (2x-1)