If a boy runs 125 meters north, and then 75 meters south, his total displacemen5 is

 50 m

Consider the figure below: Let O be the starting reference point. The boy runs northwards 125 m and then 75 m southwards.

Displacement is the shortest path traveled from the reference point. Distance is the total path length traveled. Hence, the distance would be 125 +75 =200 m but the displacement would be .

the answer would be c