Given,

Diameter of Hemispherical Tank=3m

So, Radius of Hemispherical Tank=3/2m

Volume of Hemispherical Tank=2/3πr^{3 }

=2/3*22/7*3/2*3/2*3/2

On solving, We get Volume of Hemispherical Tank= 99/14m^{3}

Half the volume of Tank= 99/28m^{3}

Now, 1m^{3}=1000 Liters

99/28m^{3}=99000/28 Litres

This Implies, if 25/7 litres of water is emptied in 1sec,

So, 1 Litres of water will be emptied in 7/25 sec (Unitary Method of solving)

So, 1/2 the volume of Hemispherical Tank i.e.99000/28 Litres will be emptied in:

99000/28*7/25

Which is equal to=990 seconds or 16 Minutes 30 seconds.........

Hope, My answer is correct and You will understand it Easily!!