How long will it take the water tank to be filled completely?

Question

There is a huge water tank and there are four pipes that can fill the water tank.

The first pipe can fill the water tank completely in exact 2 days.
The first pipe can fill the water tank completely in exact 3 days.
The first pipe can fill the water tank completely in exact 4 days.
The first pipe can fill the water tank completely in exact 6 hours

Let's say we opened all the pipes simultaneously, how long will it take the water tank to be filled completely?

Answer 1

2 days=48 hrs
3 days=72 hrs
4 days=96 hrs
1/48+1/72+1/96+1/6=1/x --> x=288/61=4.7 hrs or 4 hrs 43 min