Pipe time question

Question

If Pipe A fills pool in 16 hours and Pipe B fills pool in 12 hours, The pool has a drain pipe that drains a full pool in 8 hours. If Pipe A, Pipe B and the drain pipe is turned on in the same time.

How much time it takes to fill the pool?

Answer 1

Its simply 1/16+1/12-1/8=1/x

So x=48 hours ans.