Two pipes A and B can fill a tank in 12 minutes and 16 minutes respectively. If both the pipes are opened together, then after how much time, B should be closed so that the tank is full in 9 minutes?

• A. \(3\frac{1}{2}\)min
• B. 4 min
• C. \(4\frac{1}{2}\) min
• D. \(4\frac{3}{4}\)