Pipe A can fill a cistern in 6 hours and pipe B can fill it in 8 hours. Both the pipes are opened simultaneously, but after two hours, pipe A is closed. How many hours will B take to fill the remaining part of the cistern
1). 2 hrs
2). $3\frac{1}{3}$ hrs
3). $2\frac{2}{3}$ hrs
4). 4 hrs