Lens Maker: Compute the focal length of a lens from its index of refraction and radii of curvatures of the two refracting surfaces.
If the index of refraction of the glass utilized is 1.50, one surface is concave and has a radius of curvature of 13.4 {\rm cm} and the other surface is convex and has a radius of curvature of 22.0 {\rm cm} the focal length of the lens is