An observer stands on the bank of a river, and looks directly across the river to a tree on the opposite bank. The angle of elevation from the feet of the observer to the top of the tree is 30 degrees. If the river is 20 feet wide, how tall is the tree? Do not round until you reach your answer, and then round your answer to the nearest tenth of a foot. Answer with a numeric value only. That is, do not include "ft" or "feet" in your response.