Let ABCD be the cross-section of the canal with AB = 10 m, CD = 8 m.
Let h be the height of the trapezium ABCD. Then,
Area of trapezium ABCD
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It is given that the area of cross-section of the canal is 72 m .
Therefore, 9h = 72
h = 8 m
Hence, the depth of the canal is 8 m.
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