I'm very great-full if you get this far and actually read my question.

Just so you know this is not a homework question. I have my own sole trader business, nothing to do with maths but this question will be used as part of future R/D work for myself. I am rubbish at maths but I try very hard to muddle through. I really appreciate the help if you offer any.

The equation I am trying to solve is the following.

I have an air/water mix ratio (AW)

I know how long it takes to fill a vessel (T) so I'm left with just water with a set AW ratio eg 99% air 1% water takes a time = 4 (T = 4)

What I need to work out is how to reverse the calculation

So I know that and AR of 99 results in a T or 4

What would be the formula to work out what AR is based on a change to T

EG AR of 99 Expected time T = 4

Found a T of 3.8 What is actual AR?

Again really appreciate if you can help. Happy to buy a few coffees for anyone who can help

Tim