4. Water is being poured into a conical tank 10 feet high having a diameter of 10 feet at the top. If the rate of flow is 5 cubic feet per minute, what is the rate at which the water level is rising when the water level is 6 feet above the bottom? 5. A kite in the air at an altitude of 400 feet is being blown horizontally at the rate of 10 feet per second away from the person holding the string at the ground level. At what rate is the string being let out when 500 feet of string are already out? 6. A 10 foot plank is leaning against a wall. The bottom of the plank is being pushed toward the wall at the rate of 6 in/sec. How fast is the acute angle that the plank makes with the ground increasing when the bottom of the plank is 2 feet from the wall? 7. A heap of rubbish in the shape of a cube is being compacted into a smaller cube. Given that the volume decreases at a rate of 2 cubic meters per minute, find the rate of change of an edge of the cube when the volume is exactly 27 cubic meters. What is the rate of change of the surface area of the cube at that instant