A plane mirror is in front of shaving in which he can see his image. It is approaching towards him at a speed of 3 m s${}^{-1}$. At what speed will his image approach him?

Let distance of object from the mirror be $x$. So, distance between object and the image will be $2x$. Since mirror is moving towards the object, the distance between object and the mirror after one second is $(x-3)$. So, distance between object and its image will be $(2x-6)$. So, in the second the distance between object and image changes by a distance of $6m$. So, speed with which image approaches shaving man is $6m{s}^{-1}$.