mph means Miles Per Hour, so 21 miles takes 21/60=.35 hour. Then .35 hour is equal to .35*60=21 minutes.
So the final answer is 21 minutes
30 minutes.
31 minutes.
36 minutes
18 minutes
20 minutes !
About 45 minutes
about an hour 40 minutes
30 minutes.
10 Minutes
36 minutes
31 minutes.
18 minutes
40 minutes.
That would be 53 hours, 36 minutes
20 minutes !
About 27 minutes, 45 seconds.
About 43 minutes.