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Explanation:
Ignoring the variables for now, the GCF of 18 and 12 is 6. This is the largest factor found in both values
Now let's consider the variables. Both terms have an 'x' in them, but not a y. This means x will be tacked on the 6 we found earlier to get the overall GCF to be 6x.
Note how
18x + 12xy = 6x*3+6x*2y = 6x(3+2y)
Showing we can factor out the GCF using the distributive property.