2x2 + 14xy -36y2 = (2x+2By)(x - 2y)
2x2 + 14xy -36y2 = 2x2 -4xy +2Bxy -4By2
2x2 + 14xy -36y2 = 2x2 + (2B-4)xy -4By2
since the coefficient of y2 is equal so
-4B = -36
B = 9
if you want to make sure subs in coeeficient of xy by B=9
and you'll get 14 so the answer is right
B=9
