Two pipes A and B can fill a tank in 36 min and 45 min respectively. Pipe C can empty it in 30 min, A and B are opened and after 7 min, C is also opened. In how many minutes will the tank be full?

1. 49 minutes
2. 47 minutes
3. 46 minutes
4. 39 minutes

Explanation: The tank will be full in 46 minutes.