PhysicsLAB: The Librarian

Words cannot express how J. Jr. feels about his latest heartthrob, Miss Ova Dew, the librarian. Good looks, a great personality, and a cover-girl complexion make her the most checked-out item in the entire library. Unfortunately for J. Jr., she is a bit too popular. Every time he asks her for a date, she is already booked. She always seems to be in circulation. J. Jr. even resorts to unique ways of asking for dates. For example, he intentionally returns all his books two weeks late and then asks if she would like to go out and spend the fine together. Once again, though, his novel idea turns into a short story when she says "no." Today, however, is going to be different. He is on his way to meet her at her request. Not for a date, mind you, but rather to help her learn about projectors and how they work. (He is hoping to become her personal audiovisual aid.) Her first question concerns the way in which the projector forms images.

If the film and the screen are 4 meters apart and the image on the screen is magnified 24 times, what is the position and the focal length of the lens?

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