US Airlines receives an average of 500 calls per hour from customers who want to make reservations, where the times between calls follow an exponential distribution.

It takes an average of 3 minutes to handle each call. Each customer who buys a ticket contributes $100 to US Airlines profit. It costs $15 per hour to staff a telephone line. Any customer who receives a busy signal will purchase a ticket from another airline. How many telephone lines should US Airlines have? Base your answer on an appropriate simulation. Does it matter whether the service times are exponentially distributed or gamma distributed? Experiment to find out.