Concept:A plane mirror forms an image that moves at the same speed as the object, but in the opposite direction relative to the mirror.Explanation:The man moves toward the plane mirror at 6m/s.His image also moves toward the mirror at 6m/s.So the separation between the man and his image reduces at the sum of their speeds.v=6m/s+6m/s=12m/s.Thus, the distance between the man and his image changes at 12m/s.Answer:12m/sCorrect option: C.