28500 - 23700 = 4800
2008 - 2005 = 3
so in 3 years, it went down 4800......that means it went down (4800/3) = 1600 per year
so in 2012....which is (2012 - 2005) = 7 years...it would have gone down :
7 * 1600 = 11200
so the value of the car in 2012 is : (28500 - 11200) = 17,300 <==