Fast Clips is a walk-in barber shop/hair salon serving the general public on a first-come, first-served basis (no appointment needed). The shop has three chairs, each staffed by a barber/stylist. Customers arrive at the rate of 7.2 per hour, according to a Poisson distribution. The time required for each cut will vary, but averages 20 minutes.

a. On average, how many customers are in the shop (total waiting and being served)? b. What is the average number of customers waiting to have their hair cut and styled? c. What is the average time a customer will wait before being seated in the barber chair? d. What is the average total time that a customer spends in the shop?