square parking lot 250m side surface lot planar sloping one

a square parking lot of 250m on a side. the surface of the lot is planar, sloping to one of its edges. along the downstream edge is a gutter, this gutter drains the entire lot and is sloped from both ends toward a sewer inlet at its center. the time of concentration of the lot is estimated to be 20 min, of which 18 min accounts for overland over the lot surface and 2 min accounts for travel down each half of the gutter.assuming the rational formula is applicable with a runoff coeeficient of 0.75 which of the following storms will yield the highest peak runoff? what will be the peak runoff rate in each case? a)100mm/h for a duration of 10min b) 25mm/h for a duration of 40min c)15mm/h for a duration of 66.7 min