The fundamental frequency of a closed tube that is 35 centimetres long is approximately 246.4 Hertz, assuming sound is traveling at 345 metres per second. The formula for obtaining this number is f(1)=nv/4L.
In this case, the fundamental frequency, or f(1), equals the number of the frequency, n, times the velocity, v, divided by four times the length of the tube. In this problem, n=1 because it is the fundamental, and the length is given as 35 centimetres, or 0.35 meters. The velocity, 345, is an example of a common number, but it may change. Simplifying, the problem becomes f(1)=(1x345)/(4/0.35). Further, it becomes f(1)=345/1.4, which equals around 246.4.