Here is how i calculated

Volume of discharges - 30 litres
There is 3.6 litres of water added to the 30 litres
Then
100ml sample taken from the discharges (30+3.6) and then spun in a centrifuge = 60% solids in tube is the result

Now if i remove the 3.6 litres of water i should get 67% solids...i used this below

Calculated = 60*(30+3.5)/30

I need to know if this is the correct answer and then how to set up in a spreadsheet please

Thanks for any help

Paul