Two rays travelling parallel to the principal axis strike a large plano-convex lens having a refractive index of 1.60. If the convex face is spherical, a ray near the edge does not pass through the focal point and spherical aberration is said to have occurred. If this face has a radius of curvature, R of magnitude 20.0 cm and the two rays are h1=0.5 cm and h2 = 12.0 cm from the principal axis, find the difference in positions where they cross the principal axis.