The left face of a biconvex lens has a radius of curvature of magnitude 12.0 cm, and

Question:

The left face of a biconvex lens has a radius of curvature of magnitude 12.0 cm, and the right face has a radius of curvature of magnitude 18.0 cm. The index of refraction of the glass is 1.44.
(a) Calculate the focal length of the lens.
(b) What If? Calculate the focal length the lens has after is turned around to interchange the radii of curvature of the two faces.