15m/s * 1km/1000m*60s/1 min*60 min/1hr=
You do the calculation.
Here are the conversions used in the conversion.
1km = 1000 m, 60 seconds = 1 minute, 60 minutes = 1 hour.
When you set up the problem the 15 meters is in the numerator and 1 second is in the denominator. To convert the 15 meters to km the next conversion factor needs to have 1km in the numerator and 1000 meters in the denominator. Now the 15 m will be divided by 1000 m which cancels the meters and leaves km.
The seconds in 15 m/s is in the denominator so to convert seconds to hours multiply by 60 seconds placing it in the numerator over 1 minutes. Use the same idea to set up the conversion from minutes to hours.
Practice this conversion. It is a fundamental conversion that any middle school student should know how to do.