Answer
$$0.279 mols$$
Work Step by Step
Divide masses provided by the molecular mass of the molecule/element to find the mols.
Molar mass of $N_2O = 2\times(14.01, mass of nitrogen) + (16, mass of oxygen) = 44.02 gN_2O$
$\frac{12.3g N_2O in sample}{44.02gN_2O per mole} \approx 968mol N_2O$