First you need to get a carton and cut off the top. Cut the carton in half the long way. Then you need cut a small hole in the middle of one of the short sides of the carton. This is going to be where the balloon is going to go. Put the balloon throught the hole, but you don’t need to blow it up yet. Make some holes on each side of the carton for the axles and put straws through these holes. Make sure you put them close to the bottom. Attach the spools to the straws and put pins through the straws to keep the spools on. Last you blow up the balloon, don’t tie the end of it and let it go so your car will go.