in short, the average rate of change is plainly the slope of the set, so we can pick any two points off there, say 2, 35 and 10, 115,
[tex]\bf (\stackrel{x_1}{2}~,~\stackrel{y_1}{35})\qquad
(\stackrel{x_2}{10}~,~\stackrel{y_2}{115})
\\\\\\
% slope = m
slope = m\implies
\cfrac{\stackrel{rise}{ y_2- y_1}}{\stackrel{run}{ x_2- x_1}}\implies \cfrac{115-35}{10-2}\implies \cfrac{80}{8}\implies 10[/tex]
