Answer:
3
Step-by-step explanation:
you can set up a ratio using corresponding parts from each triangle.
or
notice the change from 3 to 9 is by multiplying 3 x 3
the change is the same for all : 3 x 4 = 12 , 3 x 5 = 15
ratio way
[tex]\frac{new}{old\\}[/tex] = [tex]\frac{9}{3}[/tex] = 3
