Resposta :
[tex]p/V=80\;km/h\rightarrow V_m=\dfrac{\Delta S}{\Delta t}\Longrightarrow 80=\dfrac{8}{\Delta t}\Longrightarrow \Delta t=0,1\;h=6\;min\\\\\\
p/V=100\;km/h\rightarrow V_m=\dfrac{\Delta S}{\Delta t}\Longrightarrow 100=\dfrac{8}{\Delta t}\Longrightarrow \Delta t=0,08\;h=4,8\;min\\\\\\
Tempo\;que\;economizaria:\\\\ 6-4,8=\boxed{1,2\;min}[/tex]