Final answer:
An athlete can run 240 kilometers in an hour.
Step-by-step explanation:
To find out how many kilometers an athlete can run in an hour, we can use the conversion factor of time. There are 60 minutes in an hour, so if the athlete can run 12 kilometers in 3 minutes, we can set up a proportion to find out how many kilometers he can run in an hour:
12 kilometers / 3 minutes = x kilometers / 60 minutes
Cross-multiplying, we get 3x = 12 * 60, so x = (12 * 60) / 3 = 240 kilometers.
Therefore, the athlete can run 240 kilometers in an hour.