Can someone tell me what sort of equation I would use for this question, I can't use the magnification as I have two unknowns. At least I don't know how to apply the magnification equation to this question. A microscope is made in a tube 25.0cm long. It magnifies 5.00 x 10 to the 2 times, 50.0 times by the objective lens and 10 times by the eyepiece. What is the focal length of the two lenses?