The GCF of 72 and 36 is: 36
List out the factors of each number (72 and 36), and find the common factors between the two numbers.
Factors of 36: 1, 2, 3, 4, 6, 9, 12, 18, 36
Factors of 72: 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72
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.