First, lets' see all the points that are plotted on the preimage and match them to the corresponding points on the image.
A(-4,5) | A'(4,5)
C(-5,1) | C'(-5,1)
T(-1,3) | T'(1,3)
We notice in the x-coordinates of each point and it's corresponding point that it becomes negative (for example, on point A, the x-coordinate is 4 and on point A', th point is -4). Therefore, we can write the rule (x,y) -> (-x,y).
(The "->" is an arrow)
:)
