Physics - Geometrical Optics Question with Solution | TestHub

In an experiment a convex lens of focal length$15 \mathrm{cm}$is placed coaxially on an optical bench in front of a convex mirror at a distance of$5 \mathrm{cm}$from it. It is found that an object and its image coincide, if the object is placed at a distance of$20 \mathrm{cm}$from the lens. The focal length of the convex mirror is-