One hour and thirty minutes
Assuming that X represents the number of hours worked and f(x) the number of cars washed, the equation would be f(x)=11x+14x.
The 11x represents the number of cars washed by Arianna in x number of hours and the 14x represents the number of cars washed by Matthew in x number of hours. You add the two because they are each washing their own car at their own pace but working on one lot.
