Ok, so
We got the following monomials.
We have to find the greatest common factor of the previous monomials.
For this, let's go by the numbers first.
The maximum number which could divide 3, 6, and 21 at she same time is 3.
So, 3 is a number common factor.
Now, let's go with variable g.
The maximum exponent that "g" has is 1. And it could divide the rest of the monomials. Then, g is a term of the common factor.
Now, we notice that h^2 is the maximum term which could divide the rest of h terms.
Finally, the greatest common factor will be 3gh^2