[tex]\bf f(3)=12\iff
\begin{cases}
x=3\\
y=12
\end{cases}\qquad thus
\\\\\\
\begin{array}{lllll}
&x_1&y_1\\
% (a,b)
&({{ 3}}\quad ,&{{ 12}})\quad
% (c,d)
\end{array}
\\\quad \\
% slope = m
slope = {{ m}}= \cfrac{rise}{run} \implies 5
\\ \quad \\\\
% point-slope intercept
y-{{ y_1}}={{ m}}(x-{{ x_1}})\qquad \textit{plug in the values and solve for "y"}\\
\textit{ } \uparrow\\
\textit{point-slope form} [/tex]
