$($c$)$ The water table in a farm is to be dropped by $12$ cm in $3$ days. The hydraulic conductivity of the soil is $0\mathrm{.}70$ m$/$day$,$ the equivalent depth is $2$ m $,$ while the equivalent drainable porosity is $0\mathrm{.}05.$ The water table mid$-$way between drains is initially $30$ cm below the soil surface. If the depth of the drain to the drain axis is one meter. Find the drain spacing. $(10)$