[tex]\bf \begin{array}{lllll}
&x_1&y_1&x_2&y_2\\
% (a,b)
&({{ -2}}\quad ,&{{ 15}})\quad
% (c,d)
&({{ 9}}\quad ,&{{ -18}})
\end{array}
\\\\\\
% slope = m
slope = {{ m}}= \cfrac{rise}{run} \implies
\cfrac{{{ y_2}}-{{ y_1}}}{{{ x_2}}-{{ x_1}}}\implies \cfrac{-18-15}{9-(-2)}\implies \cfrac{-18-15}{9+2}
\\\\\\
\cfrac{-33}{11}\implies -3[/tex]
[tex]\bf \stackrel{\textit{point-slope form}}{y-{{ y_1}}={{ m}}(x-{{ x_1}})}\implies y-15=-3[x-(-2)]
\\\\\\
y-15=-3(x+2)\implies y-15=-3x-6\implies y=-3x+9[/tex]
