ANSWER
[tex]0\operatorname{km}[/tex]EXPLANATION
First, let us make a sketch of the question:
From the diagram:
=> black line represents North
=> green line represents East
=> blue line represents West
=> red line represents South
From the diagram, we see that at the end of his journey, he returns to his start point.
Since displacement is the measure of the change in the position of an object and the boy's position did not change after the journey, his displacement is:
[tex]0\operatorname{km}[/tex]