Sumy is working in geometry class and is given figure ABCD in the coordinate plane to reflect. The coordinates of point D are (a, b) and she reflects the figure over the line y = x. What are the coordinates of the image D’?

Sumy is working in geometry class and is given figure ABCD in the coordinate plane to reflect. The coordinates of point D are (a, b) and she reflects the figure over the line y = x. What are the coordinates of the image D’?