(Solved by Experts): Pipe A can fill a tank in 10 minutes. Pipe B can fill the same tank in 15 minutes. Pipe C at the bottom of the tank is a waste pipe for emptying the tank. After opening Pipe A and Pipe B, a man returns when the tank should have been full. However, he finds that Pipe C was also kept open and shuts it and the tank overflows in the next 2 minutes. How many minutes will Pipe C take to empty the tank if Pipes A and B are kept shut?