A driver of a car stopped at a gas station to fill up his gas tank. He looked at his watch, and the time read exactly 4 : 45 4:45 p.m. At this time, he started pumping gas into the tank. At exactly 4 : 50 4:50, the tank was full and he noticed that he had pumped 12.5 12.5 gallons. What is the average rate of flow of the gasoline into the gas tank