Answer:
4=side length of A'B'
4 is length of B'B.
Explanation:
the dilation is 1/3. 9 is the bottom side length of the bigger triangle and 3 is the corresponding one of the smaller triangle. 9/3=3. 12/3=4
4=side length of A'B'
2 times 3 equals 6 (BC')
6-2=4
4 is length of B'B.