def calculate_unladen_mass(curb_mass, fuel_mass):
    """
    Calculate unladen mass [kg].

    :param curb_mass:
        Curb mass [kg].
    :type curb_mass: float

    :param fuel_mass:
        Fuel mass [kg].
    :type fuel_mass: float

    :return:
        Unladen mass [kg].
    :rtype: float
    """
    return curb_mass + fuel_mass
