Resonance Tube

A tuning fork is in unison with an air column of length 20 cm in a resonance tube experiment . If another identical resonance tube, whose length is more by 1 cm than the first tube is used , then 4 beats/second are heard with the same tuning fork. What is the frequency of the tuning fork ?

A tuning fork is held a little above the open end of a resonance tube. Resonance is heard when the length of air column are respectively. 24 cm and 74.1 cm. Calculate the end-correction and diameter of the tube.