A golden rectangle is one of the most visually appealing of all geometric forms. The Parthenon, built by the Greeks in the 5th century B.C., fits into a golden rectangle if its ruined triangular pediment is included. In a golden rectangle, the length l and width w must satisfy the equation below. If a rectangular billboard is to have a width of 30 feet, what should its length be so that it is a golden rectangle? (Give your answer correct to 1 decimal place.)

l / w = w / (l - w)

l = _____ feet