How many cubes on needed to build the ninth figure?
1st: 4 cubes
2nd: 7 cubes
3rd:10 cubes
The pattern is increasing by 3 cubes for each figure.
4 + 3 = 7 cubes
7 + 3 = 10 cubes
10 + 3 = 13 cubes
Therefore, to build the ninth figure, 13 cubes are needed.