The histogram shows information about the total time, $$\(m\)$$ minutes, taken by each child in a school to walk to school every day for one week. There are no children for whom $$\(m> 100\)$$ There are 10 children for whom $$\(m \leqslant 20\)$$ Work out an estimate for the number of children for whom $$\(50< m \leqslant 80\)$$

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