def add(vec_1, vec_2):
    """
    This function performs vector addition. This is a good place
    to play around with different collection types (list, tuple, set...),

    :param vec_1: a subscriptable collection of length 3
    :param vec_2: a subscriptable collection of length 3
    :return vec_3: a subscriptable collection of length 3
    """

    # add two vectors
    vec_3 = [float(vec_1[0]) + float(vec_2[0]), float(vec_1[1]) + float(vec_2[1]), float(vec_1[2]) + float(vec_2[2])]

    return vec_3