4 A fast-food restaurant has one drive-through window.

An average of 40 customers per hour arrive at the window.

It takes an average of 1 minute to serve a customer. Assume that interarrival and service times are exponential.

a On the average, how many customers are waiting in line?

b On the average, how long does a customer spend at the restaurant (from time of arrival to time service is completed)?

c What fraction of the time are more than 3 cars waiting for service (this includes the car (if any) at the window)?