An electric utility company operates two thermal power plants, A and B, using three different grades of coal, C, C, and C3. The minimum power to be generated at plants A and B is 30 and 80 MWh, respectively. The quantities of various grades of coal required to generate 1 MWh of power at each power plant, the pollution caused by the various grades of coal at each power plant, and the costs of coal are given in the following table: Coal type C C2 C3 Quantity of coal required to generate 1 MWh at the power plant (tons) A 2.5 1.0 3.0 B 1.5 2.0 2.5 Pollution caused at power plant A 1.0 1.5 2.0 B 1.5 2.0 2.5 Cost of coal at power plant A 20 25 18 B 18 28 12 Formulate the problem of determining the amounts of different grades of coal to be used at each power plant to minimize (a) the total pollution level, and (b) the total cost of operation.