A hemi-spherical tank of radius \(1.61\) \(m\) is full of water. It is connected with a pipe which empties the tank at the rate of \(7\) litre per second. How much time will it take to empty the tank completely?
 
Answer:
 
Volume of the tank is given by cu.units.
 
The volume of the hemispherical tank is \(l\).
 
Time taken to empty the tank \(=\)  minutes
  
[Note: Round off the minutes to whole number.]