The transformation RO - 180° means rotation of - 180°.
That is half-turn clockwise.
When you apply that rotation, the coordinates of a point (x,y) transforms into coordinates (-x,-y).
So, any coomposition that is equivalent to half-turn will produce the same image as RO - 180°.
These are some examples:
1) RO 90° and RO 90° (because 90° + 90° = 180° and that is equivalent to -180°).
2) RO - 90° and RO - 90° (because - 90° - 90° = - 180°).
3) RO 90° and RO - 270° (becasue 90° - 270° = - 180°).
At the end there are infinite combinations equivalent to Ro - 180°, so, given that you did not include the set of choices, I have provided the explanations and examples which teachs you how to test any combination of rotations.
