The answer is 0 because if you apply force in both sides, it will not move. The force should be in one side only so that it would create the so called Motion. For better understanding, try this: Get a box or something big then have another person help you do this work. Put your hands on the RIGHT side of it then tell the other person to put his/her hands in the LEFT side of it. Together, put force into the box by pushing it, It will not move :)