Answer
$\approx$751.953 mi/hr
Work Step by Step
We have to convert 343 m/s to miles/hour using conversion factors.
Since 1 mile = 1609 meters, 343 m/s = (353/1690) mi/s
Since there are 60 seconds in a minute, and 60 minutes an hour, therefore there are 3600 seconds in an hour.
To convert (353/1690) mi/s to mi/hr, multiply by 3600
(353/1690) * 3600 $\approx$ 751.953 mi/hr