During lunchtime, customers arrive at a postal office at a rate of lambda equals 36 per hour. The interarrival time of the arrival process can be approximated with an exponential distribution. Customers can be served by the postal office at a rate of mu equals 45 per hour. The system has a single server. The service time for the customers can also be approximated with an exponential distribution. What is the probability that at most 4 customers arrive within a 5-minute period