def _Backward2b_T_Ps(P, s):
    """Backward equation for region 2b, T=f(P,s)

    Parameters
    ----------
    P : float
        Pressure, [MPa]
    s : float
        Specific entropy, [kJ/kgK]

    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 26

    Examples
    --------
    >>> _Backward2b_T_Ps(8,6)
    600.484040
    >>> _Backward2b_T_Ps(90,6)
    1038.01126
    """
    I = [-6, -6, -5, -5, -4, -4, -4, -3, -3, -3, -3, -2, -2, -2, -2, -1, -1,
        -1, -1, -1, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 2, 2, 2, 3, 3, 3,
        4, 4, 5, 5, 5]
    J = [0, 11, 0, 11, 0, 1, 11, 0, 1, 11, 12, 0, 1, 6, 10, 0, 1, 5, 8, 9, 
        0, 1, 2, 4, 5, 6, 9, 0, 1, 2, 3, 7, 8, 0, 1, 5, 0, 1, 3, 0, 1, 0, 1, 2]
    n = [316876.65083497, 20.864175881858, -398593.99803599, -
        21.816058518877, 223697.85194242, -2784.1703445817, 9.920743607148,
        -75197.512299157, 2970.8605951158, -3.4406878548526, 
        0.38815564249115, 17511.29508575, -1423.7112854449, 1.0943803364167,
        0.89971619308495, -3375.9740098958, 471.62885818355, -
        1.9188241993679, 0.41078580492196, -0.33465378172097, 
        1387.0034777505, -406.63326195838, 41.72734715961, 2.1932549434532,
        -1.0320050009077, 0.35882943516703, 0.0052511453726066, 
        12.838916450705, -2.8642437219381, 0.56912683664855, -
        0.099962954584931, -0.0032632037778459, 0.00023320922576723, -
        0.1533480985745, 0.029072288239902, 0.00037534702741167, 
        0.0017296691702411, -0.00038556050844504, -3.5017712292608e-05, -
        1.4566393631492e-05, 5.6420857267269e-06, 4.1286150074605e-08, -
        2.0684671118824e-08, 1.6409393674725e-09]
    Pr = P / 1
    sigma = s / 0.7853
    T = 0
    for i, j, ni in zip(I, J, n):
        T += ni * Pr ** i * (10 - sigma) ** j
    return T
