SMT shopping mall has a single sale counter and, customers arrive according to Poisson probability distribution. The time required to pay the goods customers follows an exponential probability...

Extracted text: SMT shopping mall has a single sale counter and, customers arrive according to Poisson probability distribution. The time required to pay the goods customers follows an exponential probability distribution. The mean arrival rate is 12 customers per hour, and the mean service rate is 18 customers per hour. What is the average number of customers in the system? 6 customers Ob 2 customers OC3 customers Od.4 customers