Answer
(a) Trip takes $1.43\,\mathrm{h}$.
(b) We save $0.33\,\mathrm{h}$.
Work Step by Step
Conversion - $1\,\mathrm{mile}=1.609\,\mathrm{km}$.
(a) Distance traveled, $d=150\,\mathrm{km}$.
Speed, $s=65\,\mathrm{mi/h}=104.59\,\mathrm{km/h}$.
Time taken,
\begin{align*}
t&=\frac{d}{s}=\frac{150}{104.59}\\&=1.43\,\mathrm{h}
\end{align*}(b) Return speed, $s'=85\,\mathrm{mi/h}=136.76\,\mathrm{km/h}$.
Time taken,
\begin{align*}
t'&=\frac{d}{s'}=\frac{150}{136.76}\\&=1.1\,\mathrm{h}
\end{align*}Time saved is $(t'-t)=(1.43-1.1)=0.33\,\mathrm{h}$.
