Stoichiometry!
the chemical formula for baking powder is nacho3. how much of each reactant is needed to create 6oz of baking powder? ?

Now,  if i remember this correctly, since i havent had a chemistry class in over 6 or so years

first you want the mass of baking powder in SI units,
why? -- well because molar mass unit conversions are generally in grams per mole
now, 1 oz = 28.3495 grams

now, assuming the "reactants" are the sodium ion and the hydrogen carbonate ion, you need to determine how many components of each will create one component of baking powder

well, if you look at the chemical compound, it requires one Na+ and one HCO3 -
hence the conversion would be 1 mol Na+ + 1 mol HCO3- ->1 mol NaHCO3

now, the big question is
I have 6oz of NaHCO3, but how many moles is that equal to?

now this is where molar mass is required (if you dont know what a mole is, i suggest looking it up, it has to do with a number of atoms in order to get a specific value)

now, the atomic weight of a sodium ion is 23 au
therefore the Molar mass of a sodium ion is 23 g/mol
the atomic weight of HCO3 is 61 au (i think)
hence the molar mass (MM) is 61 g/mol
the atomic weight of NaHCO3 is 84 au
hence the MM of NaHCO3 is 84 g/mol

now going back to the balanced equations
1 mol Na+ + 1 mol HCO3- ->1 mol NaHCO3
1 +1 ->1

but if we multiply each mol by its respective molar mass, we get
23 g Na+ + 61g HCO3-  -> 84g NaHCO3

from here, if you wanted to find the amount of each "reactant" in oz,
its just a bunch of proportions