This is not an exponential function. If you were to graph this out, you would see a parabola forming. Or at the very least, a parabolic-like curve forms. An exponential curve only increases or only decreases for the entire domain. However, in this case, we have an increasing portion, and then it decreases.
This is an exponential function. Each time x increases by 1, y is multiplied by 4. The equation that models these points is y = 4^x. Note how the function is strictly increasing and there are no decreasing portions mixed in.
The answer of your question is 20 gallons of gasoline. It just a simple division you just have to divide $25 which is the given money to buy an exact amount of gallon by $1.25 which is the price of each gallon. So you would come up to an answer of 20 gallons.
