In a paint plant, semiautomatic mixers are normally used. It takes 8 minutes for an operator to load a mixer with the appropriate ingredients. The mixers run automatically and dispense paint into 55-gallon drums. Mixing and unloading takes 35 minutes to complete. Mixers are cleaned automatically between batches; and it takes 5 minutes to clear each mixer. Between batches, an operator places empty drums in the magazine to position them for filling; and it takes 7 minutes to load the drums into the magazine. Filled drums are transported automatically by a conveyor to the test area before being stored. Mixers are located close enough for travel between the mixers to be negligible. (a) What is the maximum number of mixers that can be assigned to an operator without causing idle time for the mixers? (b) If Co = $ 14 / hr; and Cm = $ 27 / hr; what assignment of mixers to operators will minimize the cost per batch produced?