Customers Arrive at a Suburban Ticket Outlet at the Rate

Multiple Choice

Customers arrive at a suburban ticket outlet at the rate of 14 per hour on Monday mornings (exponential interarrival times) . Selling the tickets and providing general information takes an average of 3 minutes per customer, and varies exponentially. There is 1 ticket agent on duty on Mondays.
-What is the average number of customers waiting in line?

A) 1 633
B) 2 333
C) 2 5
D) 3 966
E) 4