A shell projected from a level ground has a range R, it does not explode. At the highest point the shell explodes into two fragments having masses in the radio 1:3 with each fragment moving horizontally immediately after the explosion. If the lighter fragment falls at a distance R from the point of projection, the distance at which the other fragment falls from the point of projection is

Question

\[\begin {array} {1 1} (a)\;2R & \quad (b)\;\frac{5R}{3} \\ (c)\;\frac{4R}{3} & \quad  (d)\;\frac{2R}{3} \end {array}\]