7.(,2.5) Allen tutors in his spare time for extra income. Buyers of his service are willing to pay $40 per hour for as many hours Allen is willing to tutor. On a particular day, he is willing to tutor the first hour for $10, the second hour for $18, the third hour for $28, and the fourth hour for $40. Assume Allen is rational in deciding how many hours to tutor. His producer surplus is A $40. B $64. C $12. D $56