Given the trinomial, what is the value of the coefficient 'b' in the factored form?

2x2 + 14xy − 36y2 = 2(x + by)(x − 2y)

b=

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