[tex]\bf (\stackrel{x_1}{10}~,~\stackrel{y_1}{14})\qquad
(\stackrel{x_2}{14}~,~\stackrel{y_2}{12})
\\\\\\
slope = m\implies
\cfrac{\stackrel{rise}{ y_2- y_1}}{\stackrel{run}{ x_2- x_1}}\implies \cfrac{12-14}{14-10}\implies \cfrac{-2}{4}\implies -\cfrac{1}{2}
\\\\\\
\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-14=-\cfrac{1}{2}(x-10)
\\\\[-0.35em]
~\dotfill[/tex]
[tex]\bf y-14=-\cfrac{1}{2}x+5\implies y=-\cfrac{1}{2}x+19\impliedby
\begin{array}{|c|ll}
\cline{1-1}
slope-intercept~form\\
\cline{1-1}
\\
y=\underset{y-intercept}{\stackrel{slope\qquad }{\stackrel{\downarrow }{m}x+\underset{\uparrow }{b}}}
\\\\
\cline{1-1}
\end{array}[/tex]
now, the x-axis has years after 1987, so 2007 is 20 years after 1987, 1987 + 20 = 2007, therefore x = 20, what is y?............[tex]\bf y=-\cfrac{1}{2}(20)+19[/tex].
and you know how much that is.
