Pipe A can fill a cistern in 4 hours and another pipe B is installed. Both the pipes together fill the cistern in $$2\frac{1}{2}$$ hours. How long will it take for B alone to fill the cistern?

A

$$6\frac{2}{3}$$ hours

B

5 hours

C

$$5\frac{1}{6}$$ hours

D

$$6\frac{3}{8}$$ hours