Answer:
The labor fee is $14.25, each quart of oil costs $2.25.
Step-by-step explanation:
Let $x be thee price of each quart of oil and $y be a flat fee for labor.
1. If the oil change for one car required 5 quarts of oil, then these 5 quarts cost $5x and together with a flat fee for labor it cost $25.50. Thus,
5x+y=25.50.
2. If the oil change for another car required 7 quarts of oil, then these 7 quarts cost $7x and together with a flat fee for labor it cost $30.00. Thus,
7x+y=30.00.
3. Subtract from the second equation the first one, then
Substitute it into the first equation:
The labor fee is $14.25, each quart of oil costs $2.25.