410. A rectangular channel 6 m wide and 3 m deep and having a bed slope as 1 in 2000 is running full. If Chezy's constant C = 54.8, pick up the correct specification of the channel from the following :

412. For a most economical rectangular channel, the hydraulic mean depth, is equal to

413. For a most economical trapezoidal open channel, the half of the top width must be equal to

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