In Virginia, the Roanoke River at Altavista on February 1, 2008, at 1500 ET had a depth of 1 m, a width of 40 m, and a flow of 20 m^3/sec. Assume that the wind speed at 10 m elevation is 4 m/sec. (a) What is the overall mass-transfer coefficient for oxygen (O2) from the atmosphere to the river? (b)Which part of the transfer mechanism controls the overall rate?