A string with a mass per length of 2.00 gm/m is stretched with a force of 120 N between two points that are 0.40 m apart. The fundamental frequency of the stretched string is in tune with the frequency of the second mode of an organ pipe filled with air and open at both ends. The velocity of sound in air at 0 degrees Celsius is 331 m/s. What is the length of the organ pipe?