Question
Carl took 3 hours to walk from Building M to Building N which was 9 km away. On his way back from Building N to Building M, he increased his average walking speed by 1 km/h. How long did he take for his journey back?
3 m

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Carl took 3 hours to walk from Building M to Building N which was 9 km away. On his way back from Building N to Building M, he increased his average walking speed by 1 km/h. How long did he take for his journey back?