Answer
-976.4 kJ
Work Step by Step
$\Delta H^{o}_{rxn}=\Sigma n_{p}\Delta H_{f}^{o}(products)-\Sigma n_{r}\Delta H_{f}^{o}(reactants)$
$=[1(\Delta H^{o}_{f,\,N_{2}(g)})+4(\Delta H^{o}_{f,\,H_{2}O(g)})]-[1(\Delta H^{o}_{f,\,N_{2}O_{4}(g)})+4(\Delta H^{o}_{f,\,H_{2}(g)})]$
$=[1(0)+4(-241.8\,kJ)]-[1(9.16\,kJ)+4(0)]$
$=-976.4\,kJ$