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 number 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. If the price to clear a garden is $30, what is Emma's profit per unit at the optimal output