def inverse_model4(Mtot,XLa,f):
    """ Calculate MA, MB, MC, and H given the other three """
    MA = Mtot * f/(1+f)
    MB = Mtot * (1-XLa-f*XLa)/(1+f)
    MC = Mtot * XLa
    H = MC/(MB+MC)
    return MA, MB, MC, H