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 15 customers per hour, what is the average length of queue waiting for servicein front of the teller? (It is a single channel, single server, single phase, unlimited waiting space model) (Note: we need Lq, not Ls - that is, the person being served is not included)