The radius of the base of a solid cone is 9 cm and its height is 21 cm. It is cut into 3 parts by two cuts, which are parallel to its base. The cuts are at height of 7 cm and 14 cm from the base respectively. What is the ratio of volume of top, middle and bottom parts respectively?
1
1 : 4 : 8
2
1 : 7 : 19
3
1 : 13 : 9
4
1 : 6 : 12