Benny the Barber $($see Question I$)$ is considering the addition of a second chail. Customers would be selested for a haircut on a FCFS basis from those waliting. Benny has assumed that both barbers would take an average of $20$ minutes to give a halreut, and that business would remain unchanged with customers armining at a rate of two per hour. Find the following information to help Benny decide lf a second chair should be added:

Part $($a$)$: The average number of customers waliting.

Part$($b$)$: The average time a customer waits.

Part $($s$)$: The average time a customer is in the shop.