Answer
39.5 cm.
Work Step by Step
The image and object distances are related to the indices of refraction and to the radius of curvature.
$$\frac{n_a}{s}+\frac{n_b}{s’}=\frac{n_b-n_a}{R}$$
$$\frac{1.45}{s}+\frac{1.60}{1.20m}=\frac{1.60-1.45}{0.0300m}$$
$$s=0.395m$$
