a) 2- The factors of 18 are 1, 2, 3, 6, 9, and 18. The factors of 8 are 1, 2, 4, and 8. This means that the greatest factor they have in common is 2.
b) 2*(9-4). You divide both 18 and 8 by their GCF. You can check this- 18-8 is 10 and 2*5 is 10. (I got the 5 from 9-4.)
