a convex lens forms a real image of a point object at a distance of 50 cm from convex lens. a concave lens is placed 10 cm behind convex lens on image side. on placing a plane mirror on the image side and facing the concave lens it is observed that final image now coincides with the object itself. find focal length of concave lens.
my attempt: v= +50cm for convex lens as real image is formed on opposite side to object.
unable to proceed further