determine how many grams of N2 are produced by 9.12 g of H2O2 and 6.90 g of N2H4. 2H2O2+N2H4= 4H2O+N2

Answer 1

This is a limiting reagent problem. I know that because amounts are given for BOTH reactants.
mols H2O2 = grams/molar mass
mols N2H4 = grams/molar mass
Convert mols H2O2 to mols N2.
Convert mols N2H4 to mols N2.
It is likely the two values for mols N2 will not agree which means one of them is not right. The correct value in limiting reagent problems is ALWAYS the smaller value and the reagent producing that value is the limiting reagent.
Then, using the smaller value, convert to grams. mols x molar mass = grams.