Since the distance hasn't changed from 4 seconds to 6 seconds, we know that the distance from the start stays the same between the time period. The object isn't moving away or moving closer at a constant speed, but is staying the same, constant distance away at a constant speed. Therefore, the object isn't moving.
Since the position doesn't change during 4-6 (remains constant at 12m) it tells us that object is not moving and remaining at constant distance from start point.