Consider the situation shown in figure. A plane mirror is fixed at a height h above the bottom of a beaker containing water (refractive index `mu`) up of a bottom formed by the mirror.

Explanation

The bottom of the beker appears to be shifted up by a distance
`/_\t=(1-1/mu)d`
Thus, the apparent distance of the bottom from the mirror is `h/_\t=h-(1-1/mu)d=h-d+d/mu`. The image is formed behind the mirror at a distance `h-d+d/mu`