The slope is 1 because the number is just x the slope would be one. If you were to plot it out on a graph as the x axis went up by 1 so would the y. To show another part if you were to use numbers from a graph two points could be (0, -2) and (1,-1). You could then find the slope by doing y2 - y1/ x2-x1. These would be -1--2/ 1-0. This would be 1/1= 1. The y's and x's would be the coordinates. x2 would be the second x coordinate, and y2 would be the second y coordinate.
Hope this helps!!=)