You have the following points:
(-15,70)
(5, 10)
In order to find the slope of the line that crosses the previous points, use the following formula:
m = (y2 - y1)/(x2 - x1)
where (x1,y1) and (x2,y2) are the given points.
replace the values of the coordinates of the points in the formula for m:
m = (10 - 70)/(5 - (-15))
m= (-60)/(5 + 15)
m = -60/20
m = -3
Hence, the slope of the line that goes trough the given points is m = -3
