4. The base of a certain solid is the circular disk x² + y² ≤ 4 in the xy-plane. Each plane perpendicular to the *x*-axis cuts the solid in an equilateral triangle. Find the volume of the solid.

2. A ladder 8 m long leans against a wall 4 m high. The lower end of the ladder is pulled away from the wall at a rate of 2 m/sec. How fast is the angle between the top of the ladder and the wall changing when the angle is 60° = π/3 radians?