Develop a model of a service station with 10 self-service pumps. Each pump dispenses each of three grades of gasoline. Customer service at the pump time is uniformly distributed between 30 seconds and two minutes. One-third of the customers pay at the pump using a credit card. The remainder must pay a single inside cashier which takes an additional 1 minute to 2 minutes, uniformly distributed. The time between arrivals of cars is exponentially distributed with mean 1 minute.