A point object is placed at a distance of 20 cm form a thin plano-convex lens of focal length 15 cm. The plane surface of the lens is now silvered. The image created by the system is at

Refraction from lens: $\frac{1}{v_1}-\frac{1}{-20}=\frac{1}{15} \therefore v=60\mathrm{cm}$ Reflection from mirror

After reflection from the mirror, the second image will be formed at a distance of 60cm to the left of lens system Refraction from lens $\frac{1}{v_3}-\frac{1}{60}=\frac{1}{15}⟵+ve$ direction

or $v_3=12\mathrm{cm}$ Therefore, the final image is formed at 12cm to the left of the lens system