Answer:
1.25 m
Step-by-step explanation:
For an open-air pipe, the two ends of the pipe corresponds to two antinodes of the standing wave; therefore, the wavelength of the wave is equal to twice the length of the tube:

We can rewrite the wavelength using the speed of the sound wave, v, and the frequency, f:

And substituting into the previous equation we get

And using
v = 340 m/s
f = 136 Hz
We find the length of the organ pipe:
