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The back of a building is a big garden. In the garden close to a building in a greenhouse, greenhouse into the garden 2m, high-3m, the greenhouse is the top of the building' s bay windows. Cleaners cleaning around the windowsill, he crossed to use a ladder greenhouse, on a garden, against a building wall. because of the greenhouse can not bear the pressure of a ladder, so the ladder is not too short. cleaners are only a 7m long ladder, do you think it can meet the requirement it? ladder to meet the requirements of the minimum length of the number?