Leak in the tank can empty the full tank in 6 hours

Inlet can fill the tank at the rate of 4 liters per minute

Work done by inlet in 1 hour$=\frac{1}{6}-\frac{1}{8 }=\frac{4-3}{24}=\frac{1}{24}$ 

Work done by inlet in 1 min$=\frac{1}{24}\times \frac{1}{60 }=\frac{1}{1440}$ 

Volume of $\frac{1}{1440}$ parts of the tank is 4 liters

$\frac{1}{1440}=4$

Upon cross multiplication,

Total capacity of the tank is 1440 x 4=5760 liters

Hence option C is correct.