The velocity of the water that flows from an opening at the base of a tank depends on the height of water above the opening. The function v(x) = √ 2gx models the velocity, v(x), in feet per second where g, the acceleration due to gravity, is about 32 feet per second squared and x is the height in feet of the water. What is the height, in feet, of the water in the tank when the velocity of the flow is 40 feet per second?