:without graphing, tell whether the line containing (6, -3) and (0, -8) is horizontal, vertical or neither.
a) neither
b) vertical
c) horizontal

In order to determine whether the line is horizontal, vertical, or neither, we need to calculate the slope [also called the gradient] of the line. The gradient is given by the formula...   
gradient = (the change in y) / (the change in x).
The change in y equals -8 - -3 = -5, and the change in x equals 0 - 6 = -6
Therefore the gradient is -5/-6, or 5/6.
For a line to be horizontal, the change in y must be 0, so the gradient is 0. And for a line to be vertical, the change in x has to be 0, so the gradient is undefined (you can't divide by 0). Science the gradient in this case is neither of these, the answer is   A) neither.

Hope this helps!