Electrostatics

Two electric dipoles of moment $P$ and $8P$ are placed in opposite directions on a line at a distance of $24$ cm. The electric field will be zero at the point between the dipoles whose distance from the dipole of moment $P$ will be $x_1$. When $8P$ is replaced by $27P$ keeping all other quantities the same, the distance $x_1$ now becomes $x_2$. The difference $|x_2 - x_1|$ is ( All the distances are measured from the centers of the dipole.)