Two bodies of masses m and 4m are placed at a distance r. The gravitational potential at a point on the line joining them where the gravitational field is zero is:\\
(1) $-\frac{4\mathrm{Gm}}{\mathrm{r}}$\\
(2) $-\frac{6\mathrm{Gm}}{\mathrm{r}}$\\
(3) $-\frac{9\mathrm{Gm}}{r}$\\
(4) zero