In the expression above, a is a constant. If the expression is equivalent to bx, where b is a constant, what is the value of b?

(4x + 4)(ax – 1) – x^2 + 4

In the expression above, a is a constant. If the expression is equivalent to bx, where b is a constant, what is the value of b?
A) -5
B) -3
C) 0
D) 12

No idea how to solve this! I tried factoring this way and that, expanding, setting everthing on left in form of x (….) + 4 = bx, but no go. Help!