Answer:
The velocity of water at the bottom, 
Given:
Height of water in the tank, h = 12.8 m
Gauge pressure of water, 
Solution:
Now,
Atmospheric pressue, 
At the top, the absolute pressure, 
Now, the pressure at the bottom will be equal to the atmopheric pressure, 
The velocity at the top,
, l;et the bottom velocity, be
.
Now, by Bernoulli's eqn:

where

Density of sea water, 



Answer:
The longest wavelength for closed at one end and open at the other is
y / 4 where y is the wavelength - that is node - antinode
The next possible wavelength is 3 y / 4 - node - antinode - node -antinode
y / 4 = 3 m y = 12 meters the longest wavelength
3 y / 4 = 3 m y = 4 meters 1 / 3 times as long