Three tank A , B and C are connected to a tank either to fill or empty the tank . All three together can fill the tank in 8 minutes whereas only A and B can fill it in 12 minutes . In a particular day all the three taps are used to fill the tank , they all are opened for 4 minutes , then A is closed , remaining 2 works for next 2 minutes then B is closed . Finally C fill the tank in 1 minute .

In how much time tap B alone can fill the tank ?