def box2start_row_col(box_num):
    """
    Converts the box number to the corresponding row and column number of the square in the upper left corner of the box

    :param box_num: Int
    :return: len(2) tuple
        [0] start_row_num: Int
        [1] start_col_num: Int
    """

    start_row_num = 3 * (box_num // 3)
    start_col_num = 3 * (box_num % 3)

    return start_row_num, start_col_num