Table 12.12 43. A city currently emits 16 million gallons (MG) of raw sewage into a lake that is beside the city. Table 12.13 shows the total costs (TC) in thousands of dollars of cleaning up the sewage to different levels, together with the total benefits (TB) of doing so. Benefits include environmental, recreational, health, and industrial benefits. ( million Gallens ) TC ( Total costs ) TB 16 MG Current Current 12 MG 50 800 8 MG 150 1300 4 MG 500 1850 TC TB OMG 1200 2000 Table 12.13 a. Using the information in Table 12.13 calculate the marginal costs and marginal benefits of reducing sewage emissions for this city. b. What is the optimal level of sewage for this city? How can you tell