Pipe P can fill 4/9 part of a tank in 28 hours and pipe Q can fill 3/5 part of the same tank in 27 hours. Both P and Q were kept open for 3 hours, then both were closed. Pipe R alone was then opened and it emptied the water in the tank in 8 hours. Pipes P, Q and R together can fill the empty tank in:
A51 hours
B57 hours
C40 hours
D42 hours