Water flows from a tank of constant cross-sectional area 60 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 it was given by the equation
2√h + (1/30)t - 2√20 = 0; 0 ≤ t ≤ 60√20.
How fast was the height of the water decreasing when its height was 9 ft?