A boy of mass 36 kg moves from one end to other end of a boat of mass 72 kg on still water. If the length of the boat is 2.7 m, the displacement of the boat is

Question

$$\begin {array} {1 1} (a)\;2.7\;m & \quad (b)\;1.35\;m \\ (c)\;5.4\;m & \quad  (d)\;0.9\;m \end {array}$$