The convex surface of a thin concave convex lens of glass of

The convex surface of a thin concave convex lens of glass of refractive index $1.5$ has a radius of curvature $20 \mathrm{~cm}$ The concave surface has a radius of curvature $60 \mathrm{~cm}$.

The convex side is silvered side and placed on a horizontal surface as shown in figure

(a) Where should a pin be placed on the axis so that its image is formed at the same place?

(b) If the concave part is filled with water (refractive index $=4 / 3$ ) Find the distance through which the pin should be moved so that the image of the pin again coincides with the pin.