Converting units involves knowing the relationship between each unit being used.
Here, both mile and meter are units of measuring distance and are related to each other by the following equivalency:
1 mile = 1609.34 meters
Similarly, both hour and second are measures of time. Each hour is composed of 3600 seconds.
That is, 1 hour = 3600 seconds
Thus, a speed of 14 miles/hour can be converted to the units of m/s by using these equivalencies as shown:
14 miles = (14 miles) x (1609.34 meters/mile) = 22,530.76 meters
1 hour = 3600 s
Thus, 14 miles/hour = (22530.76 meters / 3600 s) = 6.26 m/s
Thus, a speed of 14 miles per hour can also be expressed as 6.26 meters per second.
Hope this helps.