Remember that a point and its image are always the same distance from the centre of rotation.
Describe the rotation which moves ABCD to A'B'C'D' in this diagram.
The centre of rotation is (0, -1).
We can see that A is the same distance from (0, -1) as A'.
D is the same distance from (0, -1) as D'.
The angle of rotation is 90° clockwise.
It is possible to use constructions to find the centre of rotation, but this can be time-consuming and complicated. Try to find the centre by observation, but remember that each point and its image must be the same distance from the centre of rotation.