The correct equation is (f) = 18,000 (0.91)^x. This is due to the fact that the price of the car will depreciate (or decrease) at a rate of 9% per year. The decimal number can be calculated by subtracting 0.09 from 1 (in this case, that the car’s price is decreasing) or by adding 0.09 from 1 (if the car price is increasing, in which it isn’t in this scenario.)
