Answer: You are correct. Choice B) 6 is the answer. Nice work.
Step-by-step explanation:
If we ignore the x's for now, we have the three values: 6, -12, 18
The largest number that can go into all three of these values (aka GCF) is 6
The value 3 is a factor, but not the largest one.
There won't be any x's or x^2 terms in the GCF answer because there are no x's (or similar) in the last term 18. The x needs to show up in all three terms to have it show up in the GCF as well.