A tuning fork is used to produce resonance in a glass tube. The length of the air column in this tube can be adjusted by a variable piston. At room temperature of 27°C two successiv resonances are produced at 20cm and 73cm column length. If the frequency of the tuning fork is 320 Hz, the velocity of sound in air at 27°C is :-
(1) 330m/*
(2) 339m/*
(3) 350m/*
(4) 300m/*
