I'm primarily looking for alternative solutions, assuming my method wasn't a fluke
The stopping distance of a car is the number of feet that the car travels after the driver starts applying the brakes. The stopping distance of a certain car is directly proportional to the square of the speed of the car, in miles per hour, at the time the brakes are first applied. If the carís stopping distance for an initial speed of miles per hour is feet, what is its stopping distance for an initial speed of miles per hour?
This answer is incorrect, but I realized that multiplying it by 2 gives the correct answer (68). Is this method a fluke?