The computer is worth $1,200 after four years.
Initial price- (Initial price x Rate of decrease x amount of years), so...
3,000-(3,000x0.15x4)=3,000-1,800=1,200
Hope this helps
P.S. the 0.15 comes from 15%. With percentages you move the decimal point twice to the left so 15.0 twice to the left is 0.15 as 3.0 is 0.03
