Answer:
It is 2a
Explanation:
Ok the greatest common factor is the number and/or term common to a seri3s of values so you separate them
the GCF of 18 and 20 is 2
and you also have a and ab
now, what is common to them both
a
so you would get the gcf as 2a so it would be written as 2a(9+10b)