A person of mass $m$ is standing in the rear end of a boat of mass $5m$. Assuming the boat does have its engine turned off and put upwards. The person begins to walk over the boat as indicated until reaching the front end of the boat. Using this information. Find the length that the boat has recoiled back which the person should try either to jump or swim to reach the dock.

The alternatives given are as follows:

$\begin{array}{ll}

1.&\textrm{2 m}\\

2.&\textrm{1.2 m}\\

3.&\textrm{1 m}\\

4.&\textrm{3 m}\\

4.&\textrm{2.5 m}\\

\end{array}$

This problem kind of begs for a solution using the conservation of the center of mass. However I'm not sure if does it exist another approach. Let's say, conservation of momentum?. Can this procedure be used?. Can someone help me with this matter as well?. Please!