Point object O is placed at a distance of 20cm from a convex lens of focal length 10cm as shown in Figure., At what distance x from the lens should a concave mirror of focal length 60cm, be placed so that the final image coincides with the object?

Explanation

Object is placed at a distance of 2f from the lens (f=focal length of the lens), i.e., the image formed by the lens will be at a distance of 2f or 20cm frm the lens.
So, if the concave mirror is placed in this position, the first image will be formed at its pole and it will reflect all the rays symmetrically to the other side as shown below and the final image will coincide with the object