So first you find out how much money he makes per week, by doing 7.5 x 20 you will find that. Now you need to find how many weeks it will take, find this by dividing 1200 by the amount he makes per week and you will end up with 8.
A reduction of 15% per year means 100-15=85% reducing factor. 1st year: 0.85×18000=$15300. 2nd year: 0.85×15300=$13005. 3rd year: 0.85×13005=$11054.25. So after 3 years the value of the car is $11054.25 or $11054 to the nearest dollar.