A plane glass mirror of thickness 3 cm of material of $$\mu=\frac{3}{2}$$ is silvered on the black 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

Two converging lenses of focal length 20 cm and 40 cm are placed in contact. The effective power of the combination is

The magnifying power of a telescope is 9. When it is adjusted for parallel rays, the distance between the objective and eyepiece is 20 cm. The focal length of lenses are

A convex lens is made of 3 layers of glass of 3 different materials as in the figure.

A point object is placed on its axis. The number of images of the object are