+ b, you just have to find a and b.b is simple, it is the y coordinate where the line crosses the y axis, i.e., b=9.a is the slope of the line. This is the change in y when you take one step to the right. The change is -2.Hence y = -2x + 9
First calculate after tax tire price $390.60 / 4 = $97.65 after tax price per tire take the $97.65 divided by 90 97.65 / 90 = 1.085 1.085 is the rate of tax he paid per tire