Answer:
A'=(5,1)
Explanation:
Rotations
Given a point A(x,y) on the plane. A rotation of 270° counterclockwise will map point A to A'(y,-x), i.e. we switch x and y and invert x.
The preimage of point A is located at (-1,5). When rotated 270° counterclockwise it will map to (5,1).
The image attached below shows both points