-18
step-by-step explanation:
because mean value defines that total sum value over total number of set
54 km / hours
we need to convert seconds to hours
60 seconds = 1 minutes
60 minutes = 1hour
15 m 60 second 60 minutes
* * = 54000 meters/ hour
second 1 minute 1 hour
now we need to convert meters to km
1000 m = 1 km
54000 m 1 km
* = 54 km / hours
hour 1000m