A point charge $$q_1 = 4q_0$$ is placed at origin. Another point charge $$q_2 = -q_0$$ is placed at $$x = 12$$ cm. Charge of proton is $$q_0$$. The proton is placed on $$x$$-axis so that the electrostatic force on the proton in zero. In this situation, the position of the proton from the origin is ______ cm.