Scenario B.3 Customers Arrive at a Bank for Service,forming a Single Line

Scenario B.3
Customers arrive at a bank for service,forming a single line to wait for the first available of three tellers.They arrive at the rate of 45 per hour and are served by the first available teller,who can service customers at a rate of 20 per hour,following a Poisson distribution.Customer arrival times are governed by the exponential distribution.
-Use the information in Scenario B.3.What is the average utilization of the three bank tellers?

A) less than or equal to 60 percent
B) greater than 60 percent but less than or equal to 70 percent
C) greater than 70 percent but less than or equal to 80 percent
D) greater than 80 percent