A plano-convex lens of refractive index 1.5 and radius of curvature 30 cm is silvered at the curved face. This lens is used to from the image of an object. At what distance from the lens, an object be placed in order to obtain a real image equal to the size of the object?
(a) 20 cm
(b) 30 cm
(c) 60 cm
(d) 80 cm
