Two charges  $3\times {10}^{-8}\mathrm{C}$ and  $-2\times {10}^{-8}\mathrm{C}$  are separated by 15 cm in air. The distance of point where electric potential is zero is ( electric potential at infinity is zero)

9 cm from negative charge in between the charges 

9 cm from positive charge in between the charges

9 cm from both the charges on perpendicular bisector of the line joining the in between the charges

30 cm from positive charge outside the charges