One-fifth of a cylindrical drinking water tank is filled with water. If a water pump is on for 50 seconds, it fills 5 litres of water in the tank, and still, the tank is half empty. The total capacity of the tank is:
1
16 litres
2
15 litres
3
\(16\frac{2}{9}\) litres
4
\(16\frac{2}{3}\) litres