A plane glass mirror of thickness 3 cm of material of $\mu$= 3/2 is silvered on the back surface. When a point object is placed 9 cm from the front surface of the mirror, then
the position of the brightest image from the front surface is
 

A thick glass mirror produces a number of images.
There is an apparent shift of actual silvered surface toward the unsilvered face.
Effective distance of the reflecting surface from unsilvered face $=\frac{d}{\mu }=\frac{3}{3/2}\mathrm{cm}=2\mathrm{cm}$

Distance of the point object from effective reflecting surface = 9 cm + 2 cm = 11 cm.

Distance of image from the point object = 11 cm + 11 cm = 22 cm

Distance of image from unsilvered face = (22- 9) cm = 13 cm