Waiting Lines Impatient Customers

A gas station on a highway operates 2 gas pumps. There are several other gas stations around offering gas at similar prices. Potential customers can see if the pumps are occupied from the highway and are not willing to wait as they will move on to try another gas station.

If a potential customer arrives every 4 minutes and it takes 5 minutes to fill a car, what is the offered load on the gas station? What is the probability a potential customer moves onto another gas station?