First, you would need to find the oil costs without the labor fee. Easiest way to do this is to subtract 24.35 from 28.35, resulting in 4. 4/2 (subtract 5 from 7) gets you 2, so the oil costs $2 per quart. To get the labor, multiply 5 by 2 and subtract that value from 24.35, which gets you $14.35 for labor costs.