Get a carton and cut the top off, then cut it in half the long way. Cut one small hole in the middle of one of the short sides. This is where the balloon goes. Put the balloon through the hole but do not blow it up yet. Make some holes on each side of the carton for the axles and stick straws through these holes, and make sure you put these close to the bottom. Attach the spools to the straws and put pins through the straws to keep the spools on. Blow up the balloon but don’t tie it and let it go so the car will go.