The cost of parking in a lot can be calculated as; Cost = cost rate x time. Let the time = t. When time, t = 1 hour, Cost = 3 x 1 = $3. When time, t = 2 hours, Cost = 3 x 2 = $6. When time, t = 3 hours, Cost = 3 x 3 = $9. When time, t = 4 hours, Cost = 3 x 4 = $12. When time, t = 5, Cost = 3 x 5 = $15 (notice, $15 has exceeded $12, but the maximum cost has to be $12). Thus, the cost of parking in a lot depends on the amount of time the car is parked and not vice versa. Therefore, the amount of time a car is parked is not a function of the parking cost because time is an independent variable and the cost of parking depends on the time the car is parked