Triangle and triangle are similar. What is the measure of side ?

Answer:
10
Step-by-step explanation:
we first find out what the increase is and it is 15/9=1 2/3.
The increase is 1 2/3.
to find the "?", we do 6*increase which is 6*1 2/3.
6*1 2/3=10
the answer is 10