The equation of the linear regression line represents the relationship between the number of cars washed for charity, x, and the amount earned for the charity, y. yˆ=10x+20 what does the slope of the line represent? for every car washed for charity, the amount earned for the charity increases by $10. for every car washed for charity, the amount earned for the charity increases by $20. for every car washed for charity, the amount earned for the charity increases by $1. for every car washed for charity, the amount earned for the charity increases by $2.