In the graph, vertex S of figure RSTW has the coordinates (15,9). If RSTW is reflected across the X-axis what?

Good Morning,



I am baffled by this question and hopes someone could explain to me how the book got the answer.



Here is the link to the graph in question:



http://i42.photobucket.com/albums/e319/tomh68/HOMEWORK/RSTW.jpg



The question is:



In the graph above, vertex S of figure RSTW has the coordinates (15,9). If RSTW is reflected across the X-axis, what are the coordinates of the image of vertex W?



The book answer says it