Answer:
b
Explanation:
Displacement and distance have different meanings. Displacement is a vector quantity and is the objects overall change in position. Distance is scalar quantity which describes how much ground an object covers during motion.
If they have covered 4 miles from a origin and we don't know the origin but we know that they start there and continue for 4 miles. It will be displacement if they started at a distance and walked a certain distance and the difference from start to finish is 4 miles. Therefore, it must be distance because we don't know the initial position and only that they walked 4 miles.
Mark is right if their starting point is a origin of a coordinate system