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.
126/10 would mean that from the original number, the decimal point is at 126.0 so when it is divided by 10, it will move over one placement, making it 12.6... I would estimate that your answer is C. 12.6