We have a figure that is rotated 90° clockwise.
We have to find the rule of the transformation.
We can find the rule by applying graphically to a point (x,y):
We can see in this picture that if we rotate 90° clockwise a point (x,y), we get a tranformed point that has x-coordinates x' equal to -y and y-coordinates y' equal to x.
Then, we can write the rule as:

Answer: The rule is (x,y) --> (-y,x)