Itotally forgot how to do this and its due someone me !
(if you could explain the process for at least one i may be able to manage the rest)

I would suggest you to use this instead.
Just place the known substance for example O2 Oxygen as they are asking you, and see where the diagram takes you.
So the answer would be 2 because you’d look at the coefficients of the balanced equation up there. H2O
I hope that was helpful, if you have more questions please ask!

Abbreviated as mg-25.