def _Backward2b_T_Ph(P, h):
    """Backward equation for region 2b, T=f(P,h)

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

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

    References
    ----------
    IAPWS, Revised Release on the IAPWS Industrial Formulation 1997 for the
    Thermodynamic Properties of Water and Steam August 2007,
    http://www.iapws.org/relguide/IF97-Rev.html, Eq 23

    Examples
    --------
    >>> _Backward2b_T_Ph(5,4000)
    1015.31583
    >>> _Backward2b_T_Ph(25,3500)
    875.279054
    """
    I = [0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3,
         3, 4, 4, 4, 4, 4, 4, 5, 5, 5, 6, 7, 7, 9, 9]
    J = [0, 1, 2, 12, 18, 24, 28, 40, 0, 2, 6, 12, 18, 24, 28, 40, 2, 8, 18,
         40, 1, 2, 12, 24, 2, 12, 18, 24, 28, 40, 18, 24, 40, 28, 2, 28, 1, 40]
    n = [0.14895041079516e4, 0.74307798314034e3, -0.97708318797837e2,
         0.24742464705674e1, -0.63281320016026, 0.11385952129658e1,
         -0.47811863648625, 0.85208123431544e-2, 0.93747147377932,
         0.33593118604916e1, 0.33809355601454e1, 0.16844539671904,
         0.73875745236695, -0.47128737436186, 0.15020273139707,
         -0.21764114219750e-2, -0.21810755324761e-1, -0.10829784403677,
         -0.46333324635812e-1, 0.71280351959551e-4, 0.11032831789999e-3,
         0.18955248387902e-3, 0.30891541160537e-2, 0.13555504554949e-2,
         0.28640237477456e-6, -0.10779857357512e-4, -0.76462712454814e-4,
         0.14052392818316e-4, -0.31083814331434e-4, -0.10302738212103e-5,
         0.28217281635040e-6, 0.12704902271945e-5, 0.73803353468292e-7,
         -0.11030139238909e-7, -0.81456365207833e-13, -0.25180545682962e-10,
         -0.17565233969407e-17, 0.86934156344163e-14]

    Pr = P/1
    nu = h/2000
    T = 0
    for i, j, ni in zip(I, J, n):
        T += ni * (Pr-2)**i * (nu-2.6)**j
    return T