bond energies, solution provided

[FATIMA]

consider the following chemical reaction:

4 NH₃(g) + 3 O₂(g) = 2 N₂ (g) + 6 H₂O (g)

Use bond dissociation energies to calculate the enthalpy change for this reaction for one mole of ammonia, NH₃

some average bond energies in KJ/mol:

N-H: 389 (single)
O- -O: 498 (double bonded oxygen)
N- - -N: 946 (triple bonded)
N- -N: 418 (Double bonded)
N-N: 163 (single bond)
O - H: 464 (single bond)

what i did:

H = sum of reactants bond energies - sum of product bond energies
=[12 (389) + 3(498)] - [2(946) + 12(464)]
=(4668 + 1494) - (1892 + 5568)
=5962 - 7460
=-1498/4 since its asking for 1 mole NH₃ and there are 4 moles
= -374.5 KJ/mol

but the answer is -324.5 KJ/mol
whats wrong?