19. Water is poured into a conical funnel at the constant rate of 1 in/sec and flows out at the rate 1 of in/sec. The funnel is a right circular cone with a height of 4 in and a radius of 2 in at the base. How fast is the water level changing when the water is 2 in high? 20. A passenger ship and an oil tanker left port sometime in the morning; the former headed north, and the latter headed east. At noon the passenger ship was 40 mi from port and moving at 30 mph, while the oil tanker was 30 mi from port and moving at 20 mph. How fast was the distance between the two ships changing at that time? 21. A ladder 25 feet long is leaning against the wall of a house. The base of the ladder is pulled away from the wall at a rate of 2 feet per second. How fast is the top of the ladder moving down the wall when its base is 7 feet from the wall?