Forces and Motion - Air Rocket

*please ignore the typos in the video!*
In my neighbor's boy scout troop, they wanted to make an air rocket. They used compressed air to fire the 50g rocket vertically upward. The tube was 1.0m tall and the air exerts an upward force of 20N on the rocket as long as it is in the tube. How high does the ball go above the top of the tube?