Problem $31$: The $1-$hour unit hydrograph for a watershed is given in the figure below. A $2-$hour

storm of intensity $0\mathrm{.}5i\frac{n}{h}r$ in this watershed produces a total excess of water $($acre$-$ft$)$ of most

nearly:

$($A$)0\mathrm{.}01$

$($B$)37$

$($C$)75$

$($D$)450$