A uniform plank of length 9 m and mass 12 kg rests horizontally on a scaffold, with 1.1 m of the plank hanging over one end of the scaffold. What is the distance of the center of mass of the plank from the end of the scaffold?
1) 1.1 m
2) 4.5 m
3) 6.9 m
4) 7.9 m
