1. Let <em>y</em> represent the amount of money earned, and <em>x</em> the number of cars they wash. Then
<em>y</em> = 5<em>x</em>
Why? Each car wash costs $5. So no car washes means no earnings; 1 car wash earns $5; 2 washes earn $10; 3 washes earn $15, and so on, so that <em>x</em> car washes generate $5<em>x</em>.
2. No matter how many cars they end up washing, they will have spent $75 to set up the operation, so you subtract 75 from the equation is part (1).
3. Taking into account the setup cost of $75, the profit they make is given by
<em>y</em> = 5<em>x</em> - 75
4. When <em>x</em> = 0, meaning no cars get washed, the profit is -$75, meaning the team loses $75.
5. Set the profit function equal to 0 and solve for <em>x</em> :
5<em>x</em> - 75 = 0
5<em>x</em> = 75
<em>x</em> = 75/5
<em>x</em> = 15
So the team has to wash at least 15 cars to break even.