"Suppose you got a gift certificate to attend a concert in town. The price of admission is $40. You would be willing to pay $30 to see the concernt. Your neighbor offered to pay you $20 for the ticket. Instead, you gave it to me as a gift. How much did this gift cost you to give?"
A. $0(nothing)
B. $20
C. $30
D. $40
E. $50
F. $90