Thelma and Louise are neighbours. During the winter, it is impossible for a snowplow to clear the street in front of Thelma’s house without clearing the front of Louise’s. Thelma’s marginal benefit from snowplowing services is 12 - Z, where Z is the number of times the street is plowed. Louise’s marginal benefit is 8 - 2Z. The marginal cost of getting the street plowed is $16. Sketch the two marginal benefit schedules and the aggregate marginal benefit schedule. Draw in the marginal cost schedule, and find the efficient level of provision for snowplowing services.