Variable Costs for Pool Cleaning. During the summer, Elijah runs a pool cleaning service, and pool cleaning is a perfectly competitive industry. Assume that costs are constant in each interval; so, for example, the marginal cost of cleaning each pool from 1 through 10 is $10. Also assume that he can only clean the quantities of pools given in the table (and not numbers in between). His only fixed cost is $1,000 for the pool cleaning equipment. His variable costs include fuel, his time, and other everyday pool supplies. Which point falls on Elijah's short-run supply curve? . P = $5, Q = 10 b. P = $10, Q = 100 c. P = $60, Q = 40 d. P = $20, Q = 300