The line segment is rotated 270 degrees counterclockwise about the origin to form a'b'. which statement describes a'b'?

If we have point (x, y), rotating it 90 degrees counterclockwise amounts in the point being (-y, x). 180 degrees is (-x, -y) and 270 is (y, -x). Since A and B are made by a line connecting 2 points, we can get the 270 degree rotations of both points to get A'=(3, -1) and B'=(3, -5).