When you graph those points you can see that the slope of the line is 2.5. Since it is consistent it is very much a linear equation. This line also goes through the point (0, 0), which makes sense if you think about it...if you don't buy any cd's (0 cd's) you shouldnt be spending any money, right? The equation then for this relationship, using the fact that the y-intercept is 0, isy = 5/2 x or y = 2.5x. Either one is fine. They're exactly the same.
