Bouncing Ball

A ball is dropped 520 feet from the roof of a building. Suppose that with each bounce, the ball goes up exactly x percent of its previous height. A man who works in this building sits at his desk on the second floor, which is at a height of 15 feet above the ground. He counts as the ball passes him 17 times. Find x.

(Source: Adapted from Mathematics Teaching in the Middle School, Feb 1999)