(-5, - 1) and (5, 15) are your two originals, and you know that the equation to find the slope is:
m = (y1 - y2)/(x1 - x2)
So, if:
y1 = -1
y2 = 15
x1 = -5
x2 = 5
All you have to do is plug in the numbers:
(-1 - 15)/(-5-5)
-16/-10
8/5
so, m, or your slope, equals 8/5.