Slope can be figured out using the equation:
Y2 - Y1
----------
X2 - X1
The first point (X1, Y1) is (-1,8)
The second point (X2, Y2) is (2, -4)
So lets plug in those coordinates to the equation provided above.
-4 - 8
-------
2 - -1
Lets simplify it first.
-12
----
3
Now just divide them.
12 / 3 = 4
The slope is 4
