$5\mathrm{.}2\mathrm{.}2)$ Compute the cirical flow depth in a trapezoidal channel with a bottom width of $20$ft$,$ slop of $0\mathrm{.}0016,$ Manning's n of $0\mathrm{.}025,$ and side slopes of $2$:$1($h:v$)$ for a discharge of $400$ cfs$.$