An electronically driven loudspeaker is placed near the open end

An electronically driven loudspeaker is placed near the open end of a resonance column apparatus. The length of air column in the tube is $80 \mathrm{~cm}$. The frequency of the loudspeaker can be varied between $20 \mathrm{~Hz}$ and $2 \mathrm{kHz}$. Find the frequencies at which the column will resonate. Speed of sound in air $=320 \mathrm{~m} \mathrm{~s}^{-1}$.