Answer to Question #42020 in Optics for qwerty

Question

A concave mirror of focal length 'f1' is placed at a distance of 'd' from a convex lens of focal length 'f2'. A beam of light coming from infinity and falling on this convex lens-concave mirror combination returns to infinity. The distance 'd' must equal :
(1) 2f1 + f2
(2) –2f1 + f2
(3) f1 + f2
(4) –f1 + f2