The problem was actually being solved using the Law of conservation of momentum...
This is what I tried– I took the initial state as that of rest where both the person and the boat possesses a momentum of 0.
I took the velocity of the person as 'v' and that of the boat to be 'u' for the duration...
A boat is 4 m long and there is a person standing on one end of it. He walks across to the other end of the boat. The mass of the person is 70 kg and the mass of the boat is 200 kg. Find the distance moved by the boat.
Not very sure of my answer. Need help solving this.