Three taps A, B & C together can fill a tank in 6 hours. After working for 2 hours, A is closed and B and C filled the remaining part in 8 hours. What is the time taken for Tap A alone to fill the tank?

A,B and C working together takes 6 hours to fill the tank.  

So in one hour A,B, and C can fill  1/6 of the tank

Therefore in two hours A, B and C can fill 2(1/6) = 1/3 of the tank

So after 2 hours, 1/3 is filled and 2/3 is remaining to be filled .

But now after two hours only taps B and C are working.

and both of them takes 8 hour to fill the remaining 2/3 of the tank

B and C can fill the tank in one hour = 2/3*1/8 = 1/12

so in one hour A can fill = 1/6 - 1/12 = 1/12

So, A alone can fill the tank in 12 hours.