Two open organ pipes of lengths 60 cm and 90 cm resonate at 6^th and 5^th harmonics respectively. The difference of frequencies for the given modes…

Two open organ pipes of lengths $\displaystyle 60$ cm and $\displaystyle 90$ cm resonate at $\displaystyle 6^{\text {th }}$ and $\displaystyle 5^{\text {th }}$ harmonics respectively. The difference of frequencies for the given modes is $\displaystyle \_\_\_\_$ Hz. (Velocity of sound in air $\displaystyle =333 \mathrm{~m} / \mathrm{s}$ )