Graft Hair Salon has three barbers to provide service in a neighborhood of downtown of Santa Fe. Customers arrive at a rate of 8 customers per hour, and the average service time of each person is 15 minutes. The interarrival time and service time of customers are exponentially distributed. With the average service time being 15 minutes, the owner of the hair salon wants there to be no more than a 10% chance that a customer will be placed on hold. How many barbers should the hair salon have