The time barber Joe takes to give a haircut is exponential with a mean of 12 minutes. Because of his popularity, customers arrive randomly (Poisson) at a rate much higher than Joe can handle: six per hour. Joe will feel comfortable if the arrival rate is effectively reduced to about four customers per hour. To accomplish this goal, he came up with the idea of providing limited seating in the waiting area in hope of encouraging newly arriving customers to go elsewhere when all seats are taken. How many seats should Joe provide to accomplish his goal?