A trolley is moving horizontally with a constant velocty of `v m//s` w.e.t. earth. A man starts running from one end of the trolley with velocity `1.5v m//s` w.r.t. to trolley. After reaching the opposite end, the man return back and continues running with a velocity of `1.5 v m//s` w.r.t. the trolley in the baclward direction. If the length of the trolley is L then the displacement of the man with respect to earth during the process will be :-