For these types of problems, You must look at the coefficients and variables separately and find the GCF for each. Then, combine the two
First, take 12 and 9
Factors of both
9- 1, 3, 9
12- 1, 2, 3, 4, 6, 12
So the gcf of 12 and 9 is 3
Now do the variables a and a^2
a^2 is just a twice
The GCF is a
Now combine a and 3
Answer: GCF is 3a