Question
Xuan and Charlie have a bicycle race. Xuan cycles at a speed of 18 km/h. Charlie cycles at a speed of 21 km/h. If Charlie lets Xuan start 40 min before him, how long will Charlie take to catch up with Xuan?
3 m

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Xuan and Charlie have a bicycle race. Xuan cycles at a speed of 18 km/h. Charlie cycles at a speed of 21 km/h. If Charlie lets Xuan start 40 min before him, how long will Charlie take to catch up with Xuan?