To make this a linear equation, you would do this:
It starts off already of you spent $25, even with 0 miles, so the y-intercept would be 25.
The slope would be .40x, while x = additional miles.
In the slope intercept form, it would be y = .40x + 25
The graph would be: https://puu.sh/zPyHV/880c02e660.png
