For a certain organ pipe, the first three resonance frequencies are in the ratio of \( 1:3:5 \) respectively. If the frequency of fifth harmonic is \( 405\,\text{Hz} \) and the speed of sound in air is \( 324\,\text{m}\,\text{s}^{-1} \) the length of the organ pipe is _____ \( \text{m} \)
