A concrete$-$lined rectangular canal $($n $=0\mathrm{.}012)$ is $5$ m wide and $2$ m deep and laid on a slope of $1$ per $4000.$ What is the savings in:

$31$Lining per km length $($m$2)$ if the most efficient proportion for rectangular canal was used for the same discharge, material and bed slope?

$32.$ Lining per km length $($m$2)$ if the most efficient proportion for trapezoidal canal was used for the same discharge, material and bed slope?

$33.$ Earth excavation $($m$3)$ if the most efficient of all section was used for the same discharge, material and bed slope?