The fourth coordinate point would be at (1, 1). If you look at the graph, it's easy to see which point is missing. You can also tell by looking for the x and y values that don't repeat, since this is a rectangle. -6 is an x-value for two coordinate points, but 1 is an x-value for only one. 10 repeats as a y-value in two coordinate points, but 1 only appears once.
