Correct Answer - Option 2 : 4 hours
CONCEPT:
In situations where both the rates of the inlet pipes and the outlet pipes are given or can be calculated, always take the capacity as the LCM of both of them or any whole number which is a multiple of the LCM.
CALCULATION:
Let the capacity of the tank be 12 liters
The amount of the tank filled by inlet pipe in an hour = 6 liters
The amount of the tank emptied by outlet pipe in an hour = 2 liters
The amount of the tank emptied by the leak in an hour = 1 liter
Amount of the tank filled after 1 hour = 6 - 2 - 1 = 3 liters
∴ time taken to fill the tank = 12/3 = 4 hours
For all the questions like this try to take a whole number of assumptions instead of variables, it will make the calculations a whole lot easier.