A swimming pool is fitted three pipes. The first two pipes working simultaneously, fill the pool in the same time as the third pipe alone. The second pipe alone fills the pool 5 hours faster than the first pipe and 4 hours slower than the third pipe. In what time will the second and third pipes together fill the pool ?
1) 3 hours 2) 3.75 hours 3) 4 hours 4) 4.75 hours 5) None of these