Answer: 1/3
Explanation:
First think of what is the GCF (greatest common factor of 6 and 18) the answer is 6. because the factors of 6 are 1,2,3,6. the factors of 18 are 1,2,3,6,9,18. they both share 1,2,3, and 6. so those are common. but GCF is asking for the greatest one, so 6 is the GCF.
Divide the top and bottom by 6:

Numerator: 6/6 = 1
Denominator: 18/6 = 3
So the final answer is 1/3