Hi!
If the initial price is $80,000 and the final price is $20,000. The difference can be found by working out the total difference:
80,000 - 20,000 = 60,000.
If it decreases at a contant rate over the space of 5 years, the amount per year can be worked out by dividing the difference between the two prices and the length:
60,000 รท 5 = 12,000.
This means that every year the car decreases in price by $12,000.
This means that

!
Hope this helps!