Time is most frequently the independent variable. It should go on the x axis. This question is no exception.
The account balance is the dependent variable and should go on the y axis.
You can only pick one of these and a couple are absurd. Time goes on the x axis and the account balance goes on the y. We care nothing about what the interest rate creating the increase.
The answer is C
Let the average cost of car in 2009 be $x, then the average cost of a car in 2013 is 2x - 5
25,000 = 2x - 5
2x = 25,000 + 5 = 25,005
x = 25,005/2 = $12,502.50