We could have really used that other number. Without that, the answer will be one of the factors of 28.
The GCF is 28.
The GCF is 4.
The GCF is 1.
The GCF is 4.
The GCF is 14.
The GCF is 28.
The GCF is 2.
The GCF is 14.
The GCF is 2.
The GCF is 28.
The GCF is 4.
The GCF is 2.