Looking at the factors above, the common ones are 1, 2, 3, 4, 6, 9, 12, 18, and 36. But... considering we are looking for the "greatest" common factor, our highest number out of the listed ones is 36, making it the greatest common factor of 72 and 36.
this would never really happen in my opinion the height and diameter would decrease. but if it takes 8 for 4 the it should take 2 for 1 because it looks like its doubling