Let's consider an example of a call center that takes orders for a mail order business. During the peak period, the average time between call arrivals (Xa) is 0.5 minute with a standard deviation (Sa) of 0.203 minute. The average time to service a call (X) is 4 minutes and the standard deviation of the service time (S,) is 2.5 minutes. If the call center is using 9 operators to service calls, how long would you expect customers to wait before being serviced? What would be the impact of adding an additional operator?