What is the image point of (0,-9)(0,−9) after the transformation T_{2,-4}\circ r_{y=x}T 2,−4 ​ ∘r y=x ​ ?

Answer 1

I am not sure what your notation means, but my best guess is:

Reflection of (0,-9) yields (-9, 0)

Translation of (-9,0) 2 units to the right and 4 units down gives us the point (-7, -4)