Multiply 
and verify the answer for x = 1 and y = 2
= - 3x3y3bx + 
x2y4bx
= -3x4y3b + 
x3y4b
According to question:
When x = 1 and y = 2
= - 3 (1)4 (2)3 b + 
(1)3 (2)4 b
= - 3 (8) b + 3 (8) b
= 0
18
Multiply and verify the answer for x = 1 and y = 2
= - 3x3y3bx + x2y4bx
= -3x4y3b + x3y4b
According to question:
When x = 1 and y = 2
= - 3 (1)4 (2)3 b + (1)3 (2)4 b
= - 3 (8) b + 3 (8) b
= 0