Twelve Customers Arrive at the Lunch Counter at George's Happy

Multiple Choice

Twelve customers arrive at the lunch counter at George's Happy Hog per hour and select the hickory smoked meat du jour along with a side and soda for $5. The server doubles as the cashier and can take and fill an order in three minutes on average. What is the lowest number n such that the likelihood of n or more customers in line and receiving service is 0? Assume that the arrival and service times can be assumed as exponentially distributed.

A) one
B) two
C) three
D) four