Displacement is given by the minimum distance between the initial and final position of a particle.
In the given case, all the girls start from point P and reach point Q. The magnitudes of their displacements will be equal to the diameter of the ground.
Radius of the ground = 200 m
Diameter of the ground = 2× 200 = 400 m
Hence, the magnitude of the displacement for each girl is 400 m.
This is equal to the actual length of the path skated by girl B.