Q$27)$ A rectangular open channel has a rough concrete lining $(n=0\mathrm{.}017)$ and conveys a discharge of $22\mathrm{.}0m\frac{3}{s}.$ If the channel bottom slope is $0\mathrm{.}01,$ then the hydraulically most efficient cross$-$sectional dimensions, including $0\mathrm{.}5m$ freeboard, are:

Mannting equation: $Q=\frac{1}{n}A{R}^{\frac{2}{3}}{S}_B^{\frac{1}{2}}$

a $1\mathrm{.}5m$ high and $3\mathrm{.}0m$ wide

b $2m$ high and $3\mathrm{.}5m$ wide

c $2m$ high and $3m$ wide

d $3m$ high and $2m$ wide