Step-by-step explanation:
The distance traveled varies directly with the time spent in motion. If d is distance and t is time taken. Then,
[tex]d\propto t[/tex]
or
[tex]d=kt[/tex]
k is the constant of variation
If d = 150 miles and t = 4 hours
[tex]k=\dfrac{d}{t}\\\\k=\dfrac{150}{4}\\\\k=37.5\ mph[/tex]