(a) You're using a 20-cm-focal-length convex lens to image a small light bulb. Where should you place the bulb to get a half-size real image? (b) A movie projector uses a single lens to project a real image on a screen 6 m from the lens. Each frame of the movie film is 3 cm tall, and the image is 1.2 m tall. How far should the film be from the lens?