For the following questions answer them individually
A trapezoidal channel has a bottom width of 6m and side slope of 1:1. The depth of flow is 1.5 m at a discharge of 15 cum/sec. The hydraulic radius and hydraulic average depth of flow respectively are
If 2% solution of a sewage sample is incubated for 5 days at 20 degrees and depletion of oxygen was found to be 5 ppm, BOD of the sewage is