There is a barber shop with only one barber working. The capacity of the shop is 4 customers (including the one getting service). A new customer arrives in every 24 minutes on average, and the average service time is 15 minutes. Both arrival time and service time are exponentially distributed random variables. a) Find the service rate assuming that the shop is always open. b) How much would the service rate increase if the capacity is increased to 5 customers (including the one getting service)