You need at least two numbers to find a GCF.
The GCF is 3.
The GCF is 17.
The GCF is 3.
The GCF is 1.
The GCF is 1.
The GCF is 1.
The GCF is 3.
The GCF of 42 and 51 is 3.
The GCF for 29 51 is 1.
The GCF of 39 and 51 is 3.3
The GCF is 1.
The GCF is 1.