The car goes up a 13--high hill, then descends 18 to the track's lowest point. You've determined that the spring can be compressed a maximum of 2.

The car goes up a 13--high hill, then descends 18 to the track's lowest point. You've determined that the spring can be compressed a maximum of 2.3 and that a loaded car will have a maximum mass of 440 . For safety reasons, the spring constant should be 13 larger than the minimum needed for the car to just make it over the top