(Table: Variable Costs for Garden Maintenance) Use Table: Variable Costs for Garden Maintenance. During the summer, Emma runs a gardening service in a perfectly competitive industry. Assume that costs are constant in each interval; so, for example, the marginal cost of clearing weeds from each of the gardens 1 through 10 is $20. Also assume that she can only tend to the numbers of gardens given in the table (and not numbers in between). Her only fixed cost is $1,000 for a weeding machine. Her variable costs include fuel, her time, and hot coffee. What is Emma's shut-down price in the short run? Table: Variable Costs for Garden Maintenance Quantity of Lots Variable Costs 0 $0 10 200 20 300 30 500 40 750 50 1,100 60 2,100 a. $15 b. $50 c. $42 d. $20