Problem:
Define the operation "∘" by x∘y=4x−3y+xy, for all real numbers x and y. For how many real numbers y does 3∘y=12?
Answer Choices:
A. 0
B. 1
C. 3
D. 4
E. more than 4
Solution:
Substituting 3 for x yields 3∘y=12−3y+3y=12. Thus 3∘y=12 is true for all real numbers y.