To factor the expression \(6x + 18x^2\), we first need to identify the greatest common factor (GCF) of the terms.
The GCF of \(6x\) and \(18x^2\) is \(6x\).
Now, we factor \(6x\) out of the expression:
\[ 6x + 18x^2 = 6x(1 + 3x) \]
So, the expression \(6x + 18x^2\) can be rewritten by factoring out the GCF as:
\[ 6x(1 + 3x) \]