A discharge of 2,200 ft^3/sec flows in a trapezoidal channel at a normal depth of 8.0 ft. The channel has a slope of 0.01, a 12-ft bottom width, and side slopes of 1:1 (H:V). Determien the manning coefficient of channel roughness. Also determine the sensitivity range of the roughness coefficient estimate if the flow rate can only be estimated to within +/- 200 cfs.