[" 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) "-(6Gm)/(r)," (2) "-(9Gm)/(r)],[" (3) Zero "," (4) "-(4Gm)/(r)]]