91Ó°ÊÓ

Given that the height of the pencil is $h=9cm$and the distance between the tip and the mirror is $s_{tip}=12cm$and between the end of the eraser and mirror is $s_{eraser}=21cm$as shown in the figure below

For the plane mirror, the distance of object$s$ is the same for the image $s\text{'}$.

The ratio between the distance of object and the distance of image is called lateral magnification and is given by

$m=-\frac{s\text{'}}{s}=-1$

The negative sign represents the direction of the image which is behind the mirror. So, the length of the image of the pencil that is formed is $h\text{'}=9cm$.

The tip of the head has an image formed at the same length 12cm and the image of the end of the eraser is formed at 21cm . So, the tip of the head is closer to the mirror surface as shown in the diagram.