Customers Enter the Waiting Line to Pay for Food as They

Customers enter the waiting line to pay for food as they leave a cafeteria on a first-come,first-served basis.The arrival rate follows a Poisson distribution,while service times follow an exponential distribution.If the average number of arrivals is four per minute and the average service rate of a single server is seven per minute,what proportion of the time is the server busy?

A) 0.43
B) 0.57
C) 0.75
D) 0.25
E) 0.33