If in 2 years, your car is worth $15000, then x2 so then you’ll make it 4 years. $15000+$15000= $30000 but then you’ll have to know what the last year is so since in 2 year your car turned $15000 more then you divide it by 2 which is $7500. Then, you add $15000+$15000+$7500 which is $37,500.
