Answer:
Here is the solution . see the attached file
Divide 20 by 4=5
then 5 by 7=5/7
k=5/7
In 7 years, the car was 18,000 and after 5 years it is worth 10,500 so if you subtract 18000-10500=7500 and if you do 7500/5=1500 so this means that the car was going down 1500 in value every year.
D 8x-3 because must add them all together