There are three tellers working each day in the SunTrust Bank on Sage Road. Customers arriving at the branch can be categorized into two groups. The first group of customers usually requires simple tasks, such as depositing checks and withdrawing cash. On the other hand, the second group of customers requires more complicated services, such as money orders, wire transfers, new account, mortgage refinancing, etc. Currently, one teller is assigned to serve the first group of the customers who form a single line. The second group of customers is served by the other two tellers in a separate line (i.e., a two-server queue). The service time for the first group is 3 minutes per customer, and follows an exponential distribution. For the second group, the average service time is 30 minutes with a standard deviation 15 minutes. The arrival rate arrival rate of the first group is 15 customers per hour, whereas the arrival rate for the second group is 3 customers per hour. Assume both groups of customers arrive according to a Poisson process