What is the reflection image of p (0, 0) after two reflections, first across x = -3 and then across y = -3?

Reference the image below if you need to.

We start at red point (0,0) and reflect across blue line x= -3.
This puts the point equidistance away on the opposite side at blue point (-6, 0).
That point is then reflected across green line y= -3,
and ends up at green point (-6, -6).