Suppose a convex lens is ground so that one surface has a radius of curvature of 30.0 cm and the opposing surface has a radius of curvature of 40.0 cm. The focal length is 34.2cm. What is the index of refraction of the lens? What kind of glass is the lens? Need help by using the formula 1/f=(n-1)(1/R1+1/R2).