The graph above shows the total cost, $C$, in dollars, of purchasing $G$ gallons of gasoline. The relationship between the number of gallons and the total cost is proportional. The graph shows a line passing through the origin $(0,0)$ and the point $(10,35)$, where the x-axis represents the number of gallons ($G$) and the y-axis represents the total cost ($C$) in dollars. What is the cost per gallon of gasoline, in dollars?