An organ pipe open at both ends has length 0.60 m and vibrates in its third harmonic. A pipe closed at one end emits a note that is 30 Hz lower than this in its fundamental mode. If the speed of sound in air is 340 m s−1, determine the length of the closed pipe.
a) 8.5\;\text{cm}
b) 20.8\;\text{cm}
c) 10.4\;\text{cm}
d) 14.6\;\text{cm}