In an open organ pipe \( \nu_3 \) and \( \nu_6 \) are \( 3^{\text{rd}} \) and \( 6^{\text{th}} \) harmonic frequencies, respectively. If \( \nu_6 - \nu_3 = 2200 \,\text{Hz} \) then length of the pipe is ________ \( \text{mm} \). (Take velocity of sound in air is \( 330 \,\text{m/s} \).)
