Pipe V1 can fill an empty tank in 8 hours. Pipe V2 can fill the same tank in 16 hours. Pipe V3 can empty the same, completely filled, tank in 12 hours. If three pipes are opened simultaneously, then in how much time will the tank get completely filled?

Pipe V1 = 8 hours 

Pipe V2 = 16 hours

Pipe V3 = -12 hours (negative sign represents for emptying)

Let's assume the capacity of the tank is 48 units.

Efficiency of Pipe V1 = $$\frac{48}{8}$$ = 6 units/hour

Efficiency of Pipe V2 = $$\frac{48}{16}$$ = 3 units/hour

Efficiency of Pipe V3 = $$\frac{48}{-12}$$ = -4 units/hour (negative sign represents for emptying)

Therefore,total time for the tank to get filled = $$\frac{48}{6+3-4}$$

= $$\frac{48}{5}$$ hours