A tube of length L1=35 cm has other internal L2=43.7 cm that allow stretching or compressing the tube to modify its length, as shown in the figure. A tuning fork is placed in front of the tube emitting waves at frequency F. As the inner tube is slowly withdrawn, the sound of the tuning fork creates standing waves in the tube as the total length is 46.1 cm, 57.625 cm and 69.15 cm. Assume that the system is at a temperature of 23C. The frequency with which the tuning fork emits waves is: