Point O is the center of dilation. Triangle A B C is dilated to create triangle A prime B prime C prime. The length of O A is 3. The length of A A prime is 9.
 Triangle ABC is dilated to create triangle A'B'C' using point O as the center of dilation.
 What is the scale factor of the dilation?
 1/3
 3
 4
 1/4