A trapezoidal channel with bottom width $b=8$ and side slopes of $z=2H$:$1V$ and a slope of $0\mathrm{.}0100$ is carrying a flow of $106\mathrm{.}3cfs.$ The Mannings $n$ value is $0\mathrm{.}050.$ For one step of the backwater calculations the known downstream depth is $1\mathrm{.}64.$ The calculated depth $3\mathrm{.}0ft$ upstream is

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$($answer in feet to $2$ decimal places$).$