Without hyperfine interaction, the levels are all equidistant and so:
∆E_0 = g * µ_B * B_0 = 0,11576764 meV.
HFF, so now also perturbations. EPR selection rules dictate that ∆m_J=1 and ∆m_I=0, so ∆E_pert = ±A/2.
A = g * µ_N * B_HF / J = 2,1016342×10^-7 eV, so ∆E_0 ± ∆_pert = 0,1159778 meV or 0,1155575 meV.