A luminous point object is moving along the principal axis of a concave mirror of focal length 12 cm towards it. When it's distance from the mirror is 20 cm it's velocity is 4 cm/s. The velocity of the image in cm/s at that instant is?
1. 6 towards the mirror
2. 6 away from the mirror
3. 9 towards the mirror
4. 9 away from the mirror