First we have to know how much of one hour is 20 min.
To get it, we have to dividie 20min by 60 min (60 min=1hour), so
20:60=\(\frac{20}{60}= \frac{2}{6}= \frac{1}{3}\)
We know that
\(v= \frac{s}{t}\)
where v is velocity, s is distance and t is time
We can modify formula to get
\(v= \frac{s}{t} \\ v*t=s\)
Now we just have to substitute our data ( t=1/3 and v=9 miles/hour)
s=\(\frac{1}{3}*9\)=3 miles - its the result
