def mark_board(board: list[list[str]], winning_numbers: list, winning_number_index: int):
    """Marks a board if a number matches a winning number."""
    for line_index, line in enumerate(board):
        for num_index, num in enumerate(line):
            if num == winning_numbers[winning_number_index]:
                board[line_index][num_index] = (
                    num + 'X'
                )  # We append an 'X' here to know we've marked it, we'll later remove it to get our answer
        # print(line)

    return board