The statement that must be true about the two postal delivery workers is:
They each have a displacement of 0 miles.
This is because displacement is defined as the change in position from the starting point to the final point. Since both workers start and end their routes at the post office, their displacement is zero.
However, their distance traveled can vary based on their individual routes, and they will likely have different velocities depending on their speeds and routes. Therefore, the other statements are not necessarily true.