Related rates - Ladder slides, with Chain rule discussion (Matheno.com)

Related rates problem & solution, with extra Chain rule discussion: "A 10-foot ladder leans against a wall. The base of the ladder slides horizontally away from the wall at 2 feet per second. As a result, the top of the ladder moves down the wall. At what rate is the top of the ladder sliding down the wall when the base is 8 feet from the wall?" Let's solve this together, and illustrate the approach you can use to solve EVERY related rates problem you're given.