A string with a mass per length of 2.00 g/m is stretched with a force of 120 N between two points that are 0.400 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 at 20C and open at both ends. The speed of sound in air at 0C is 331 m/s. What is the length of the organ pipe