Triangle rst was transformed using the rule (x, y) → (–x, –y). the vertices of the triangles are shown.

r (1, 1) r' (–1, –1)
s (3, 1) s' (–3, –1)
t (1, 6) t' (–1, –6)

which best describes the transformation?

the transformation was a 90° rotation about the origin.
the transformation was a 180° rotation about the origin.
the transformation was a 270° rotation about the origin.
the transformation was a 360° rotation about the origin.