First of all we designed the car keeping in mind few factors i.e. the outer design, a chamber for reaction, the direction and way car moves.

We used acrylic plates as base of the car and a bottle as reaction chamber that will have a small hole to diffuse the gas that will in result produce the motion of car. (The hole will be closed using a screw)

Then we added 100 ml vinegar to bottle attached to car. Then 50 ml water as well

Next we added 7 gram of Baking Soda and closed the cap. Shake the bottle well until a large froth forms.

 Lastly keep the car down and open the small hole in the cap that we closed with a screw previously. 

The gas will diffuse and car will move in opposite direction.