With unaided vision, a person can focus on objects that lie at distances between 5.0 m and .5 m away from his eyes. Find the focal lengths of each part of the bifocal eye glasses lenses that will give him normal vision, able to focus on objects at 25cm to infinity. Assume the glasses are 2cm from his eyes. If each part of these bifocal lenses is convex-concave (a.k.a. ophthalmic) with the radius on the side closest to the eye of 18.6cm, what should the two radii be on the side farthest from the eye? The lens is made of Trivex, a light plastic, and has in index of refraction of 1.53. Please Explain.