Showing Transformation is True

I'm confused by this question:

Quote:

A transformation

**T** in the plane consists of a reflection in the line x + y = 0 followed by a translation in which the point (x,y) is transformed to the point (x+h,y+k).

(a). Show that the matrix representing

**T** is

$\displaystyle \begin{bmatrix} 0 & -1 & h \\ -1 & 0 & k \\ 0 & 0 & 1 \end{bmatrix}$

The question only mentions x and y so I assume this is supposed to be an $\displaystyle R^2$ transformation but the matrix is a 3x3.. don't see how the multiplication would work.

I tried transforming the unit square but didn't do much to help me understand.

Thanks