We assume that an oil spill is being cleaned up by deploying bacteria that consume the oil at 4 cubic feet per hour. The oil spill itself is modeled in the form of a very thin cylinder whose height is the thickness of the oil slick. When the thickness of the slick is 0.001 foot, the cylinder is 500 feet in diameter. If the height is decreasing at 0.0005 foot per hour, at what rate is the area of the slick changing?