Which of the following best represents the average speed of a fast runner?

10 meters per second

10 miles per minute

10 centimeters per hour

10 kilometers per second

For the answer to the question above, the easiest way to determine is changing every runner's speed into the same unit.

First = 10 m/s 

Second = 10 miles/min = 16090.34 / 60 m/s (As 1 mile = 1609.34 meter and 1 min = 60 sec) 
Second = 260.82 m/s 

Third = 10 cm/hr = 10*(0.01)/60*60 (As 1 cm = 0.01 m and 1 hr = 60*60 sec) 
Third = 0.000028 m/s 

Fourth = 10 km/sec = 10*1000 m/s (As 1 km = 1000 m and time is already in sec) 
Fourth = 10000 m/s 

So fastest would be the one who covers the largest distance in 1 sec. It would be the fourth one.