Water flows from a tank of constant cross-sectional area 30 ft2 through an orifice of constant cross-sectional area 1.4 ft2 located at the bottom of the tank. Initially, the height of the water in the tank was 20 ft, and t sec later is given by the equation ,_ 2v"? + T15: zv' = o o s t s 3ov'2o. (D Differentiate the given equation with respect to t. dh _ dt How fast (in ft/s) was the height of the water decreasing when its height was 4 ft? ft/s