John drives 1000 miles a month.  He needs to get an oil change every 3000 miles.  He gets 1 free oil change a year.  If an oil change costs $50, how much does he pay a year?
He needs to get an oil change every 3000/1000 = <T>divide(3000, 1000)=3.0 months
So he gets 12/3 = <T>divide(12, 3)=4.0 oil changes a year
That means he pays for 4-1 = <T>subtract(4, 1)=3 oil changes a year
So he pays 3*$50 = $<T>multiply(3, 50)=150 a year
