Affine Transformation for Homogenous Coordinates

Hi,

I'm confused on how to reflect a matrix about a line.

The problem tells me to find a 3 × 3 matrix that produces the following composite 2D transformation by translating by (1,−6) and then reflect about the line x = −3.


I understand translation but how do you go about doing reflection?

Is there any one that can help or give me a hint?

If I first translate the problem I get

1 0 1
0 1 -6
0 0 1

I'm guessing for reflection, I need to do a conjugation? So I need to move the line from the origin to x=-3...but I'm confused about that...? Do I simply times -3 to the standard matrix of the line about x?