The number of customers coming to a bank between 1:00 and 1:30 p.m. of a “normal” day has a Poisson distribution with an average of 39 customers during the half hour. The length of time each customer spends with a teller is Exponential with an average of 45.5 seconds. The average time a customer spends in the line waiting is desired to be three minutes. The manager is wondering how many tellers are required during this time period.