A manager has the responsibility to manage how tellers provide services to customers. Customers needing teller service arrive randomly at a mean rate of 30 per hour. Customers wait in a single line and are served by the next available teller when they reach the front of the line. Each service takes a variable amount of time (assume an exponential distribution), but on average can be completed in 3 minutes. The tellers earn an average wage of $18 per hour. On average, how many customers will be in the bank, including those currently being served? (Note: This is a M/M/2 problem.)