DataCom Inc. is one of the leading producers of telecommunication products located in the Pacific Northwest. It has more than 1,000 sales representatives in North America. They call orders into the central office where office workers using the central inventory control system confirm product availability, price, and delivery date. The representatives call directly from the customer’s office before signing a contract. Calls are held in a queue and served by the first available office worker on a first-come, first-served basis. Calls arrive at a rate of 55/hr (Poisson distribution) and the average time to complete the phone order is six minutes (exponential distribution). Management estimates that it costs $60 per hour to have a sales representative wait before being helped by an office worker (including the cost of having the end customers wait) and $15 per hour to employ an office worker. Determine the total expected cost per hour (representative wait costs plus office worker costs) if nine office workers are employed
a. between $130 and $140 per hour
b. between $140 and $150 per hour
c. between $150 and $160 per hour
d. between $160 and $170 per hour
e. more than $170 per hour