What is the greatest common factor of 72^2y and 18xy?

72^2y = 5184y

18xy = 18xy

72^2y factors (only some of them not All of them): 1, 2, 3, 4, 6, 8, 9, 12, 16, 18, y

18xy factors: 1, 2, 3, 6, 9, 18, x, y

Your 18xy (Option D.)

Note: Just rewrite the factors of the problem until you find out what you're looking for in the particular problem

Good Luck!