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 = <<3000/1000=3>>3 months
So he gets 12/3 = <<12/3=4>>4 oil changes a year
That means he pays for 4-1 = <<4-1=3>>3 oil changes a year
So he pays 3*$50 = $<<3*50=150>>150 a year
#### 150