Customers arrive at Rent a Wreck and hope to score an inexpensive and unsightly vehicle to use for ...

Customers arrive at Rent a Wreck and hope to score an inexpensive and unsightly vehicle to use for what typically is a short period of time.
 
  About twenty customers show up in any hour of the day and it takes the customer service representative about two minutes to photocopy their driver's license and insurance card and take an impression of a credit card. Assume that the service and arrival rates are governed by the Poisson distribution; how long does it take for the average customer to clear the system?
  A) 10 minutes
  B) 6 minutes
  C) 3.33 minutes
  D) 3 minutes