Al and Bob needed a jump start for their formula one race car. Their friend Carl could come jump the car, but the cables wouldn't reach unless they backed the car up twenty feet. The driveway was too steep for them to push it. They had plenty of rope and an old garage-door spring. So they tied some rope to the spring, tied one end to the car, pulled it tight, and tied the other end to a tree. With them and the spring pulling together, they could move it a bit. But then the spring went sproing. They tried using the jack, but couldn't rig up a way of turning push into pull. Just then, Carl pulled up. Carl is 80 years old and has a bad back. His car has plastic trim all over the place, so they couldn't tie a rope to it and use the car to pull. They don't have a wrench to disconnect the battery from either car.
How did they get the car up the hill with just their muscle power, no additional people or equipment?