A 20-foot ladder is leaning against a building. If the bottom of the ladder is sliding along the pavement directly away from the building at 2 feet/second, how fast is the top of the ladder moving down when the foot of the ladder is 3 feet from the wall?

The top of the ladder is moving down at a rate of _____ feet/second when the foot of the ladder is 3 feet from the wall. (Round to the nearest thousandth as needed.)