In the figure, a real inverted image I of an object O is formed by a certain lens (not shown); the object-image separation d = 40.0 cm, measured along the central axis of the lens. The image is exactly half the size of the object. (a) What kind of lens must be used to produce this image? (b) How far from the object must the lens be placed? (c) What is the focal length of the lens?