To solve for slope, use the equation:
slope = (y₂ - y₁)/(x₂ - x₁)
(8,1) = (x₁, y₁)
(8, -4) = (x₂, y₂)
Plug into corresponding places
(-4 - 1)/(8 - 8)
-5/0 = Undefined (because you cannot have parts over 0)
There is no slope. Unsolvable
hope this helps