What kind of figures are possible for a closed pipe?

For a certain organ pipe,three successive resonance frequencies are observed at $425 \, Hz$,$595 \, Hz$,and $765 \, Hz$ respectively. If the speed of sound in air is $340 \, m/s$,then the length of the pipe is ..... $m$.

The first overtone of the vibrating air column of a closed pipe has the same frequency as the second overtone of an open pipe $1.5 \ m$ long. The length of the closed pipe is (in $m$)

$A$ resonance tube closed at one end is of height $1.5 \ m$. $A$ tuning fork of frequency $340 \ Hz$ is vibrating above the tube. Water is poured in the tube gradually. The minimum height of water column for which resonance is obtained is . (Neglect end correction,speed of sound in air $= 340 \ m/s$) (in $cm$)

Sound waves of frequency $600 \,Hz$ fall normally on a perfectly reflecting wall. The shortest distance from the wall at which all particles will have maximum amplitude of vibration is (speed of sound $= 300 \,ms^{-1}$)

If the fundamental frequency of a closed pipe is $50\,Hz$,then the frequency of the $2^{nd}$ overtone is .... $Hz$.