Here is my thought. If 3/4ths are 6 and 1/4 is 18 then: 6+6+6+18=36. 36/4=9. That should put you at 9mg approximately if my math is correct. If you have more than 3/4th's left it will be lower, and if less than 3/4th's if will be higher. Would need to measure exactly if you want higher accuracy. Might be better to test mixing in smaller bottles first before mixing it all.
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