well, we know that the relationship of "n" and "s" is linear, so hmmm let's get their equation first.
to get the equation of any straight line, we simply need two points off of it, let's use those in the picture below.
[tex](\stackrel{x_1}{7}~,~\stackrel{y_1}{68000})\qquad (\stackrel{x_2}{9}~,~\stackrel{y_2}{76000}) \\\\\\ \stackrel{slope}{m}\implies \cfrac{\stackrel{rise} {\stackrel{y_2}{76000}-\stackrel{y1}{68000}}}{\underset{run} {\underset{x_2}{9}-\underset{x_1}{7}}} \implies \cfrac{ 8000 }{ 2 } \implies 4000[/tex]
[tex]\begin{array}{|c|ll} \cline{1-1} \textit{point-slope form}\\ \cline{1-1} \\ y-y_1=m(x-x_1) \\\\ \cline{1-1} \end{array}\implies y-\stackrel{y_1}{68000}=\stackrel{m}{ 4000}(x-\stackrel{x_1}{7}) \\\\\\ ~\hfill {\Large \begin{array}{llll} s-68000=4000(n-7) \end{array}} ~\hfill[/tex]
now, when she was hired, well that was when there were no years, namely at year 0, so we can say that's when n = 0
[tex]s-68000=4000(n-7)\implies s-68000=4000(\stackrel{n}{0}-7) \\\\\\ s-68000=4000(-7)\implies s-68000=-28000 \\\\\\ s=-28000+68000\implies {\Large \begin{array}{llll} s=40000 \end{array}}[/tex]
