Quadrilateral abcd is transformed according to the rule (x, y) → (y, –x). which is another way to state the transformation? r0, 90°

R0 means rotate by 0 degrees, or no change.
Since (x,y)->(y,-x), the quadrilateral has been rotated through -90 degrees (R-90) or R(270), or 90 degrees clockwise.
Note that by convention, all rotations are counter-clockwise.  So R90 is incorrect.

There is no graph to go along with this