Why is the answer to question c is 58.98

The registration area has just opened at a large convention of dentists in Tallahassee, Florida. One hundred dentists arrive per hour (Poisson distributed), and the cost of their waiting time in the queue is valued at $150 per person per hour. The Tallahassee Convention Center provides servers to register guests at a fee of $12 per person per hour. It takes about one minute to register an attendee (negative exponentially distributed). A single waiting line, with multiple servers, is set up. What is the minimum number of servers for this system? 2 > a. What is the optimal number of servers for this system based on evaluating waiting cost? 4 b. What is the cost waiting cost, per hour, at the optimum number of servers? [Select] c. What is the down time per server at the minimum number of servers? [Select) d. Based on the minimum number of servers, what is the average time that an attendee has to wait before being checked in, based on the number of minutes? [ Select)