A chimney flue is 15m long from the open top of the chimney to the door at the bottom of the stack that can be opened or closed from within the fireplace. When wind blows over the chimney, a low pitch sound can be heard. Assuming speed of sound is 350m/s and this sound is the air coloumn within the flue resonating at its fundamental frequency, is the dorr at the obttom of the flue opened or closed? Show all work to support your answer! Explain the logic behind your final answer.