An average of 20 cars per hour arrive at the drive-in window of a fast food restaurant, where the interarrival times are exponentially distributed. Assume that the service time for each car is exponentially distributed with a mean of 2 minutes. Due to concerns about safety, the restaurant management is considering implementation of a rule to limit the queue length to three cars. (That is, if three cars are in the waiting line for service, another car cannot enter the waiting line until the queue length is 2 or fewer.) If such a rule is instituted, what is the (long-run) percentage of time that cars will be unable to enter the queue