Pipe P and Q fill the tank in 10 hours and 15 hours respectively and pipe R can empty the tank in 12 hours. First 3- hour pipe P and Q fill the tank, then pipe P is closed and pipes Q and R fill the tank in 6 hours, then closed. Then the pipe Q alone opened to fill  for x minutes and Pipe P and Q together filled the whole tank in 2 minutes. Find the value of x