A luminous point object is moving along the principal axis of a concave mirror of a focal length 12 cm toward it. When its distance from mirror is 20 cm, its velocity is 4 cm/. The velocity of the image in cm/ at that instant is:
(A) 6 toward the mirror
(B) 6 away from the mirror
(C) 9 away from the mirror
(D) 9 toward the mirror
