=E11.23. The Security & Trust Bank employs four tellers to serve its customers. Customers arrive randomly at a mean rate of two per minute. However, business is growing and management projects that the mean arrival rate will be three per minute a year from now. The transaction time between the teller and customer has an exponential distribution with a mean of one minute.

Management has established the following guidelines for a satisfactory level of service to customers. The average number of customers waiting in line to begin service should not exceed one. At least 95 percent of the time, the number of customers waiting in line should not exceed five. For at least 95 percent of the customers, the time spent in line waiting to begin service should not exceed five minutes.