Answer: 120 hours
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Explanation:
The path is 1800 km. Kara's speed is 15 km/h. If this speed is held the same throughout the path, then it will take her d/r = 1800/15 = 120 hours to travel the entire path until she gets back to her starting point.
For Steven, it takes him d/r = 1800/30 = 60 hours to make the same journey.
The LCM of 60 and 120 is 120
Every 120 hours, both Kara and Steven will be back at the starting point together.
Note: this is a very very large time value, and this is not considering the fact that the bikers slow down or stop to take a break.
