Assuming the units on the graphs increase by 1, the points marked on the first graph are (-2, 1) and (2, -3), and the slope is -1/2; the points marked on the second graph are (-2, -2) and (3, 4), and the slope is 6/5; and the points marked on the third graph are (4, 0) and (1, -3), and the slope is -1.
Hope this helps.