At the bank teller's window, arrivals and service times are randomly distributed (Poisson and exponential distributions, respectively). There is only one teller at the window. If the arrival rate is 9 customers per hour, and the service rate is 13 customers per hour, what is the average waiting time for a customer in the system, including waiting in line and being served? Give the result in minutes. (It is a single channel, single server, single phase, unlimited waiting space model).