There are certain rules to follow when rotating a point 90 deg clockwise. Since it is given that ABCD is a parallelogram and the coordinates of point C are given, we just have to follow this simple relation:
R(90 deg) : (X,Y) ---> (-Y,X)
Using the given coordinates: R(90 deg<span>) : (-4,1) ---> (-1,-4) </span> Therefore, Point C' will be located at (-1,-4)