Answer :
Given
Speed one:
v1 = 55 mi/h
Speed two:
v2 = 75 mi/h
Distance:
x = 86 mi
Procedure
Let's calculate the times for each of the speeds.
[tex]\begin{gathered} t_1=\frac{x}{v_1} \\ t_1=\frac{86mi}{55mi/h} \\ t_1=1.56h \end{gathered}[/tex][tex]\begin{gathered} t_2=\frac{86mi}{75mi/h} \\ t2=1.14h \end{gathered}[/tex]Saving time:
[tex]\begin{gathered} t_s=t_1-t_2 \\ t_s=1.56h-1.14h \\ t_s=0.42h \end{gathered}[/tex]The total time saved is 0.42h (25.2min) by increasing the speed limit.