A tank has two outlet pipes A and B, which together take 6 hours to empty a full tank when opened simultaneously.
The tank was initially half-full and both outlets were opened.
After one hour, an inlet pipe was also opened.
If the inlet alone can fill the empty tank in 4 hours, how much time will it now take to fill the tank completely?

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.