AHSME 1993 Problem 4

Define the operation "$\circ$" by $x\circ y=4x-3y+xy$, for all real numbers $x$ and $y$. For how many real numbers $y$ does $3\circ y=12$? $\text{(A) } 0 \text{(B) } 1 \text{(C) } 3 \text{(D) } 4 \text{(E) more than 4}$