A child is playing with a large, perfectly spherical sapphire marble that has a refractive index of n = 1.77 and a diameter of 8.0 cm. She places a small figurine 4.8 cm away from the edge of the marble and notices that an image of the figurine forms on the opposite side of the marble. Consider what would happen if the marble was replaced with a thin lens that is placed where the center of the marble had been located originally and if the image remains in the same position, what would be the lens's focal length in this case?