You need at least two numbers to find a GCF.
The GCF is 4.
Since 18 is a factor of 72, it is automatically the GCF.
Since 72 is a factor of 144, it is automatically the GCF.
Since 72 is a factor of 144, it is automatically the GCF of this problem.
The GCF is 7.
The GCF is 12.
The GCF is 12.
Common factors of 28 and 42 are: 1, 2, 7, and 14.
The common factors of 72 and 86 are: 1 and 2
The common factors of 72 and 123 are: 1 and 3
2 and 4 are factors of 8. If you want them to be common, you need to compare them to another set of factors.
The common factors of 72 and 81 are: 1, 3, and 9