What is the greatest common factor of 45 and 72 explain

The greatest common factor of 45 and 72 is 9. 
45- 3 times 3 times 5 
75- 2 times 2 times 2 times 3 times 3 
3 times 3 = 9, the GCF
The GCF is 9.
Gcf of 45 and 72 is one. One is odd one is even

The greatest common factor (GCF) of 45 and 72 is: 9

Factors of 45: 1, 3, 5, 9, 15, 45
Factors of 72: 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36

The common factors between the two numbers are 1, 3, and 9, but since 9 is the highest, it is considered the greatest common factor.