Use the Following to Answer Question

Use the following to answer question:
-(Table: Variable Costs for Lawns) Use Table: Variable Costs for Lawns.During the summer,Alex runs a lawn-mowing service,and lawn-mowing is a perfectly competitive industry.Assume that costs are constant in each interval;so,for example,the marginal cost of mowing each of the lawns from 1 through 10 is $10.Also assume that he can only mow the quantities of lawn given in the table (and not numbers in between) .His only fixed cost is $1,000 for the mower.His variable costs include fuel,his time,and mower parts.If the price for mowing a lawn is $40,how much is Alex's profit per unit at the profit-maximizing output?

A) -$10.00
B) $10.00
C) $23.33
D) -$20.00