Samantha Was Willing to Pay $10 for a Hamburger Because

Samantha was willing to pay $10 for a hamburger because she was hungry but she only paid $2.50. What is the marginal benefit Samantha gained from the hamburger?

A) $2.50
B) $10.00
C) $12.50
D) $7.50
E) None of the above answers is correct.