Suppose that machines in a fatory break down with an average rate of .7 breakdowns per week. One worker can repair one machine per week. Two workers can repair a machine twice as fast. Three workers can repair a machine in one-third of the time required by one worker, and so on. Given that downtime costs $650 per week and maintenance workers are paid $300 per week, calculate the number of workers that should be employed so as to minimize the cost of downtime and repair.