Mole mass of ammonium nitrate is 80. 2 moles of NH4NO3 gives 1 mole of O2. 160 g of NH4NO3 gives 32 g of O2. Therefore 67.3 g NH$NO3 yields 32/160 x 67.3 = 11.96 g O2

Molar mass of N2 is 14. So 67.3 g NH4NO3 yields 14/80 x 67.3 = 23.55 g N2

Molar mass of H2O is 18. So 67.3 g NH4NO3 gives 72/160 x 67.3 = 30.285 g H2O.