The midpoint formula is x1+x2 over 2 and y1+y2 over 2. When you use it to find the midpoint of (0,-8) and (-4,10), you get (-2,1).
Slope formula is y2-y1 over x2-x1, which will give you -6.
Slope formula is y2-y1 over x2-x1, which will give you -6.