let's take a peek at the graph, and say get two points off the line hmmm the one on the left and the one there on the right, so (-4,5) and (8,8)
[tex]\bf \begin{array}{ccccccccc}
&&x_1&&y_1&&x_2&&y_2\\
% (a,b)
&&(~ -4 &,& 5~)
% (c,d)
&&(~ 8 &,& 8~)
\end{array}
\\\\\\
% slope = m
slope = m\implies
\cfrac{\stackrel{rise}{ y_2- y_1}}{\stackrel{run}{ x_2- x_1}}\implies \cfrac{8-5}{8-(-4)}\implies \cfrac{8-5}{8+4}\implies \cfrac{3}{12}\implies \cfrac{1}{4}[/tex]
