To assess the impact on the U.S. coal market of different pollution control strategies, the Environmental Protection Agency (EPA)14 wants to determine, for assumed control regimes, how much coal from supplies si in different mining regions i = 1,c, 24 will be extracted, how much will then be processed into various deliverable coal types m = 1,c, 8, and how much of each deliverable product will be sent to meet consumer demands dm, j in regions j = 1,c, 113. Demands are expressed in Btu, with each ton of raw coal mined at i for processing into type m yielding ai,m Btu. Including the economic burden of pollution controls and transportation, the cost per ton of raw coal mined at i for processing into type m and use at j can be estimated at ci, m, j. Formulate an LP model to determine how coal would be mined, processed, and distributed if the market seeks to minimize total cost. Use the decision variable 1i = 1,c, 24; m = 1,c, 8; j = 1,c, 1132 xi, m, j ! tons of coal mined at i for processing into m and use at j