:The relativ atommasses are to handel (addit) with (g/mol=(x)*10^-36) for the exactly molecularmass, divide it by the number of atoms and verb they paralell to the exactly ratio you want. You can to addit the sames atoms before do the paralell verbs.

It is a kind of magic sure.

Amazon.de sell an periodensystem with relative atommasses and more (study knowledge).

I like the Texas Instrument calculators (not the cheapest.)

For better, for good, God and the earth..