Britney and Paris are neighbors. During the winter, it is impossible for a snowplow to clear the street in front of Britney's house without cleaning the front of Paris's. Britney's marginal benefit from snowplowing services is 12-Z, where Z is the number of times the street is plowed. Paris'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 schedule. Draw in the marginal cost schedule, and find the efficient level of provision for snowplowing services.