A contractor, Susan Meyer, has to haul gravel to three building sites. She can purchase as much as 18 tons at a gravel pit in the north of the city and 14 tons at one in the south. She needs 10, 5, and 10 tons at sites 1, 2, and 3, respectively. The purchase price per ton at each gravel pit and the hauling cost per ton are given in the following table.
Hauling cost per ton on site
Pit 1 2 3 price per ton
North 30 60 50 100
South 60 30 40 120
Susan wishes to determine how much to haul from each pit to each site to minimize the total cost.