a convex lens of focal length 20 cm and a concave mirror of focal length 60 cm are placed coaxially facing each other at a seperation of 25 cm.A luminous object is placed at distance of 25 cm from the lens.The position of final image is

In the event that the source is at 40cm from a f=20cm focal point, at that point the picture emerges at 40 cm on the opposite side of the focal point. This picture now turns into another source on the off chance that we will mirror the question back to its unique position. On the off chance that we now include a mirror, it must be set up with the goal that ITS source and picture agree at an indistinguishable area from the picture of the focal point, i.e. at 40cm from the focal point. For a raised mirror to do this we need to compose the mirror condition as 

1−7.5=1−15+1−151−7.5=1−15+1−15 

the minuses emerging in light of the fact that the source and picture are on the correct hand side of the focal point and the negative emerging on the central length of the mirror since it is curved. Henceforth the mirror is 40–15cm=25cm from the focal point.