Final answer:
The equation to represent the total car wash earnings based on the number of cars washed is y = 9x. The independent variable is the number of cars washed (x), the dependent variable is the total earnings (y), the y-intercept is 0, and the slope is 9.
Step-by-step explanation:
To show how the total car wash earnings, y, depends on the number of cars washed, x, we can use a simple linear equation. Each car wash costs $9, so if x is the number of cars washed, then the total earnings can be calculated as 9 times x. Therefore, the equation representing this relationship would be y = 9x.
The independent variable in this situation is the number of cars washed (x), because it can vary independently. The dependent variable is the total earnings (y), because it depends on the number of cars washed. Since there is no fixed fee or starting cost, the y-intercept is 0, and the slope of the equation is 9, representing the rate at which earnings increase per car washed.