Verified Answer :

Hint: Define FACTOR.

Then, define GREATEST. And COMMON.
Put it together now.

What number do they all have in common but is the greatest number smaller or equal to them?

Simplified: x\(\ \eq\) that number.

Of course, 3.

3 because 3 goes into 3; 1 time
12 goes into 3; 4 times
18 goes into 3; 6 times
GCF is 3