The manager of Paul's fruit and vegetable store is considering the purchase of a new seedless watermelon from a wholesale distributor. Since this seedless watermelon costs $4, will sell for $7, and is highly perishable, he only expects to sell between six and nine of them. What is the payoff value for the purchase of eight watermelons when the demand is for six watermelons?

Select one:

a.10

b.21

c.24

d.17

Please provide calculation.