The Bijou Theater in Hermosa Beach, California, shows vintage movies.

Customers arrive at the theater line at the rate of 100 per hour. The ticket seller averages 30 seconds per customer, which includes selling the ticket and placing validation stamps on customers' parking lot receipts. Assume Poisson arrivals and exponential service times.   a. What is the average time customers spend in the system?   b.    What would be the effect on customer time in the system of having a second ticket taker doing nothing but placing validation stamps on customers' parking lot receipts, thereby cutting the average service time to 20 seconds?   c.    If a second window was opened with both servers doing both tasks (sell tickets and place validation stamps) and serving a single line, what is the average customer time in the system?