$2^{}$ U$.$S$.$ Labs manufactures mechanical heart valves from

the 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.TABLE $3$