A concave mirror is used in a solar cooker so that parallel rays from the Sun converge to a point 20cm in front of the mirror.
(i) Determine the focal length of the mirror, stating its sign.
(ii) Calculate the radius of curvature of the mirror.
(iii) A small rod 4cm long is placed 30cm in front of the same mirror, perpendicular to the principal axis. Find the position, nature, orientation, and length of the image of the rod formed by the mirror.