Answer:

Explanation:
As we know that the level of intensity is given as

here we know



now the sound is travelling in all possible directions so we have



now for level of sound we have


The crest of the wave has traveled 415 cm in 11.7s. then the crest should have travelled 415/11.7 cm in one second i.e. 35.47cm. Then the crest should have travelled 26*35.47 cm in 26 seconds i.e. 922.2cm which has 46 vibrations in it.
so for length of each vibration (Wavelength) is 20 cm