Winston P. 71, problems group A

heart valves of pigs. Different heart operations require
valves of different sizes. U.S. Labs purchases pig valves
from three different suppliers. The cost and size mix of the
valves purchased from each supplier are given in Table 3.
Each month, U.S. Labs places one order with each supplier.
At least 500 large, 300 medium, and 300 small valves must
be purchased each month. Because of limited availability of
pig valves, at most 700 valves per month can be purchased
from each supplier. Formulate an LP that can be used to
minimize the cost of acquiring the needed valves.