What is the power of a plane glass sheet?

$A$ ray of light $XY$ is incident on a mirror as shown in the figure. The angle of incidence for this ray is the angle between it and the line joining two other points in the figure. Name these two points and show the course of rays after reflection.

What is the mirror formula for a spherical mirror?

Which symbol is used for the refractive index?

The image formed by a concave mirror is real and of the same size. Where is the object placed?

$A$ $4.5\, cm$ needle is placed $12\, cm$ away from a convex mirror of focal length $15\, cm$. Give the location of the image and its magnification.