What are the operating characteristics of a waiting line system? Discuss.

A repairman is to be hired by a company to repair machines that break down randomly with an average of rate of four per hour for an 8-hour day. The machines wait in the queue if necessary and are repaired on a first- come- first served basis. The cost of non-productive machine time is Rs 90 per hour. The company has the option of choosing either a fast or a slow repairman. The fast repairman charges Rs 70 per hour and will repair machines at an average rate of 7 per hour, while the slow repairman charges Rs 50 per hour and will repair machines at an average rate of 6 per hour. Assuming that the pattern of machine’s breakdown is Poisson distributed and the repair time is exponentially distributed. Using the above information compare the total expected daily cost for both repairmen and advise management which repairman should be hired?