To factor the expression \( 6x + 18x^2 \) by finding the greatest common factor (GCF), we first identify the common factors in each term.
The terms \( 6x \) and \( 18x^2 \) share a GCF of \( 6x \).
Now, we can factor \( 6x \) out of the expression:
\[ 6x + 18x^2 = 6x(1 + 3x) \]
So the correct rewritten expression is:
6x (1 + 3x).
This matches with the response:
6 x left parenthesis 1 plus 3 x right parenthesis.