The given expression is

To factor it, we will find the highest common factor of 9 and 18
Since the factors of 9 are all the numbers multiplying together and giving 9, then

The factors of 9 are 1, 3, 9
We will find the factors of 18 by the same way

The factors of 18 are 1, 2, 3, 6, 9, 18
The common factors of 9 and 18 are 1, 3, 9
The greatest one is 9
Then the highest common factor of 9 and 18 is 9
Divide each term in the expression by 9

The correct expression is C [9(x + 2)]