First, let's label each coordinate of the points with x1, y1 and x2, y2
Our first point: (3, -1). 3 is x1 and -1 is y1
Our second point: (-10, 9). -10 is x2 and 9 is y2.
Slope = (y2 - y1) / (x2 - x1)
Let's plug our values into the slope formula above.
Slope = (9 - (-1)) / (-10 - 3) = 10/-13 or -10/13