d$)$ Size the surface water pipework for $12$ houses using the DATA given in the table below. $($Use a mininfor gradient of $1$:$80$ for all pipes and rainfall intensity of $50m\frac{m}{h}r)$ Give a reason for your answer.

$\backslash$table$[[$SURFACE TYPE,AREA$($A$)m^2,\backslash$table$[[$IMPERMEABILITY$],[$FACTOR $($f$)]]],[$Road or pavement,$20,0\mathrm{.}90],[$Roof$,40,0\mathrm{.}95],[$Path$,15,0\mathrm{.}75],[$Garden$,68,0\mathrm{.}25],[$Access road, parking,$25,0\mathrm{.}90]]$