Customers arrive at a barbershop according to a Poisson process at a rate of eight per hour. Each customer requires 15 minutes on average. The barbershop has four chairs and a single barber. A customer does not wait if all chairs are occupied. Assuming an exponential distribution for service times. Suppose the barber charges $12 for service. Compute the long-run rate of revenue for the barber. (Hint: What fraction of the arriving customers enter?)