check the picture below.
[tex]\bf \begin{array}{ccccccccc}
&&x_1&&y_1&&x_2&&y_2\\
% (a,b)
&&(~ -3 &,& 0~)
% (c,d)
&&(~ 0 &,& 6~)
\end{array}
\\\\\\
% slope = m
slope = m\implies
\cfrac{\stackrel{rise}{ y_2- y_1}}{\stackrel{run}{ x_2- x_1}}\implies \cfrac{6-0}{0-(-3)}\implies \cfrac{6-0}{0+3}\implies \cfrac{6}{3}\implies 2[/tex]
