bearing in mind that, there are
60 seconds in 1 minute,
60 minutes in 1 hr,
1000 meters in 1 km,
and 1.609 km in 1 mile
[tex]\bf \cfrac{40\underline{m}}{\underline{s}}\cdot \cfrac{60\underline{s}}{\underline{min}}\cdot \cfrac{60\underline{min}}{hr}\cdot \cfrac{\underline{km}}{1000\underline{m}}\cdot \cfrac{mi}{1.609\underline{km}}\implies \cfrac{40\cdot 60\cdot 60\cdot mi}{hr\cdot 1000\cdot 1.609}
\\\\\\
\cfrac{144000mi}{1609hr}\approx 89.496581\frac{mi}{hr}[/tex]
