You and your friend each start a car-washing service. you spend $25 on supplies and charge $10 per car. your friend spends $55 on supplies and charges $13 per car. how many cars do you have to wash to earn the same amount of money as your friend?

Set both equations equal to each other to solve for x ( number of cars).

10x -25 = 13x - 55

Subtract 10x from each side:

-25 = 3x-55

Add 55 to each side:

30 = 3x

Divide both sides by 3:

x = 30/3

x = 10

They will need to wash 10 cars.

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