def _Backward3b_T_Ph(P, h):
    """Backward equation for region 3b, T=f(P,h)

    Parameters
    ----------
    P : float
        Pressure, [MPa]
    h : float
        Specific enthalpy, [kJ/kg]

    Returns
    -------
    T : float
        Temperature, [K]

    References
    ----------
    IAPWS, Revised Supplementary Release on Backward Equations for the
    Functions T(p,h), v(p,h) and T(p,s), v(p,s) for Region 3 of the IAPWS
    Industrial Formulation 1997 for the Thermodynamic Properties of Water and
    Steam, http://www.iapws.org/relguide/Supp-Tv%28ph,ps%293-2014.pdf, Eq 3

    Examples
    --------
    >>> _Backward3b_T_Ph(20,2500)
    641.8418053
    >>> _Backward3b_T_Ph(100,2700)
    842.0460876
    """
    I = [-12, -12, -10, -10, -10, -10, -10, -8, -8, -8, -8, -8, -6, -6, -6,
        -4, -4, -3, -2, -2, -1, -1, -1, -1, -1, -1, 0, 0, 1, 3, 5, 6, 8]
    J = [0, 1, 0, 1, 5, 10, 12, 0, 1, 2, 4, 10, 0, 1, 2, 0, 1, 5, 0, 4, 2, 
        4, 6, 10, 14, 16, 0, 2, 1, 1, 1, 1, 1]
    n = [3.2325457364492e-05, -0.000127575556587181, -0.000475851877356068,
        0.00156183014181602, 0.105724860113781, -85.8514221132534, 
        724.140095480911, 0.00296475810273257, -0.00592721983365988, -
        0.0126305422818666, -0.115716196364853, 84.9000969739595, -
        0.0108602260086615, 0.0154304475328851, 0.0750455441524466, 
        0.0252520973612982, -0.0602507901232996, -3.07622221350501, -
        0.0574011959864879, 5.03471360939849, -0.925081888584834, 
        3.91733882917546, -77.314600713019, 9493.08762098587, -
        1410437.19679409, 8491662.30819026, 0.861095729446704, 
        0.32334644281172, 0.873281936020439, -0.436653048526683, 
        0.286596714529479, -0.131778331276228, 0.00676682064330275]
    Pr = P / 100.0
    nu = h / 2800.0
    suma = 0
    for i, j, n in zip(I, J, n):
        suma += n * (Pr + 0.298) ** i * (nu - 0.72) ** j
    return 860 * suma
