Answer: 0 m
Step-by-step explanation:
Let's begin by stating clear that movement is the change of position of a body at a certain time. So, during this movement, the body will have a trajectory and a displacement, being both different:
The trajectory is the path followed by the body (is a scalar quantity).
The displacement is the distance in a straight line between the initial and final position (is a vector quantity).
According to this, in the description Matthew's home is placed at 0 on a number line, then he moves 10 m to the park (this is the distance between the park and Mattew's home), then 15 m to the movie theatre until he finally comes back to his home (position 0). So, in this case we are talking about the path followed by Matthew, hence his trajectory.
However, if we talk about Matthew's displacement, we have to draw a straight line between Matthew's initial position (point 0) to his final position (also point 0).
Now, being this an unidimensional problem, the displacement vector for Matthew is 0 meters.