Simply graph away. Just assume that the year you bought your car was 12000, and that every year below was 1000 below. For example, if you bought your car in 2013 for $10,000 then plot the point (10000, 12000) and then maybe for the 2012 model that cost $8,000 plot the point (8000, 11000) and so on and so forth. At the end you will take a screen shot of your graph so be careful not to close the tab until you're finished graphing.