A train travels from City X to City Y and back to City X. On the way from City X to City Y, the train travels at an average speed of 60 km/h, and on the way back, it travels at an average speed of 80 km/h. If the total travel time for the round trip is 7 hours, what is the distance between City X and City Y? Let's think step by step and output the final answer within \boxed{}.
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