Thermodynamics

If the enthalpy of formation of a diatomic molecule \(\mathrm{AB}\) is \(-400 \mathrm{~kJ} / \mathrm{mol}\) and the bond dissociation energies of \(\mathrm{A}_2\) and \(\mathrm{B}_2\) and \(\mathrm{AB}\) are in the ratio \(2: 1: 2\), what is the bond dissociation enthalpy of \(\mathrm{B}_2\) ?