5. Amy, Bill, and Carla all mow lawns for money. Each of them operates a different lawn mower. The accompanying table shows the total cost to Amy, Bill, and Carla of mowing lawns.

Quantity of lawns mowed Amy’s total cost Bill’s total cost Carla’s total cost 0 $0 $0 $0 1 20 10 2 2 35 20 7 3 45 30 17 4 50 40 32 5 52 50 52 6 53 60 82

a. Calculate Amy’s, Bill’s, and Carla’s marginal costs, and draw each of their marginal cost curves.

b. Who has increasing marginal cost, who has decreasing marginal cost, and who has constant marginal cost?