Hello there!
The GCF acronym between two or more numbers means the "greatest common factor."
The greatest common factor means the highest factor two numbers have in common.
Let's factor out our numbers.
120;
1 x 120
2 x 60
3 x 40
5 x 24
6 x 20
8 x 15
10 x 12
72;
1 x 72
2 x 36
3 x 24
4 x 18
6 x 12
8 x 9
Now, let's look at the highest factors that are in common between these two numbers.
The highest factor is 12, which is your GCF.
I hope this helps!