Pipe A can fill an empty cistern in 5 hours while Pipe B lakes 6.25 hours to fill it. The two pipes are opened simultaneously when the cistern is empty, but Pipe B is turned off after some time as a result of which the cistern is filled in 3.4 hours. For how many hours was Pipe B open?

A

1.5

B

1

C

2

D

2.5