The picture below shows the formula for calculating slope
In this example:
y2 = 4
y1 = -4
x2 = 5
x1 = 3
(These are the numbers you substitute into the formula)
Calculations:
4 - (-4) = 8
5 - 3 = 2
8/2 = 4
As you can see, after the values are substituted into the equation & simplified, the slope is equal to 4