You would use 72/9 , ( division ).
Refrection of (-20, 4) across x-axis gives (-20, 4) = (-20, -4)
Refrection of (-20, 4) across y-axis gives (20, 4)
Refrection of (-20, 4) across y = -x gives (20, -4)
Refrection of (-20, 4) across y = 7 gives (20, 10)
8k-4k+4+7-k =
8k-4k-k+4+7 =
3k+11