To find the distance across a pond, Rita climbs a 30-foot observation tower on the shore of the pond and locates points [math]A[/math] and [math]B[/math] so that [math]\overline{AC}[/math] is perpendicular to [math]\overline{CB}[/math]. She then finds the measure of [math]\overline{DB}[/math] to be 12 feet. What is the measure of [math]\overline{AD}[/math], the distance across the pond?
