To factor the expression \(9z + 18\) using the greatest common factor (GCF), first, we need to identify the GCF of the terms in the expression.
The terms are:
- \(9z\)
- \(18\)
The GCF of \(9\) and \(18\) is \(9\).
Now we can factor out \(9\) from the expression:
\[ 9z + 18 = 9(z + 2) \]
So, the factored expression is:
\[ 9(z + 2) \]