In a machine shop, certain type of machines break-down at an average rate of 6 per hour. The breakdowns are in accordance with Poisson process. The estimated cost of idle machine is Rs. 15 per hour. Two repairmen A and B with different skills are being considered to be hired as repairmen. Repairman A takes six minutes on an average to repair a machine and his wages are Rs. 8 per hour, whereas the repairman B takes five minutes to repair and the wages are Rs. 10 per hour. Which repairman’s service should be used and why? Assume the work shift of 8 hours.