Answer:
18
Step-by-step explanation:
This is because when you find the prime factors, you can take out the ones that they have together.
In this case:
9 - 3 * 3
6 - 3 * 2
2 - 2
So notice that each number has a maximum of 2 3s and 1 2, thus, you can multiple 3 * 3 * 2
