\documentclass[10pt,a4paper]{article}

%% packages
\usepackage{a4wide,color,verbatim,Sweave,url,xargs,amsmath}
\usepackage{hyperref}
\usepackage[utf8]{inputenc}
\usepackage{verbatim}

%% new environments
\newenvironment{question}{\item}{}
\newenvironment{solution}{\comment}{\endcomment}
\newenvironment{answerlist}{\renewcommand{\labelenumi}{(\alph{enumi})}\begin{enumerate}}{\end{enumerate}}

%% paragraphs
\setlength{\parskip}{0.7ex plus0.1ex minus0.1ex}
\setlength{\parindent}{0em}

%% fonts: Helvetica
\renewcommand{\sfdefault}{phv}
\IfFileExists{sfmath.sty}{
  \RequirePackage{sfmath}
  \renewcommand{\rmdefault}{phv}
}{}

\newcommand{\extext}[1]{\phantom{\large #1}}
\newcommandx{\exmchoice}[9][2=-,3=-,4=-,5=-,6=-,7=-,8=-,9=-]{%
                \mbox{(a) \,\, \framebox[8mm]{\rule[-1mm]{0mm}{5mm} \hspace*{-1.6mm} \extext{#1}} \hspace*{2mm}}%
  \if #2- \else \mbox{(b) \,\, \framebox[8mm]{\rule[-1mm]{0mm}{5mm} \hspace*{-1.6mm} \extext{#2}} \hspace*{2mm}} \fi%
  \if #3- \else \mbox{(c) \,\, \framebox[8mm]{\rule[-1mm]{0mm}{5mm} \hspace*{-1.6mm} \extext{#3}} \hspace*{2mm}} \fi%
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  \if #7- \else \mbox{(g) \,\, \framebox[8mm]{\rule[-1mm]{0mm}{5mm} \hspace*{-1.6mm} \extext{#7}} \hspace*{2mm}} \fi%
  \if #8- \else \mbox{(h) \,\, \framebox[8mm]{\rule[-1mm]{0mm}{5mm} \hspace*{-1.6mm} \extext{#8}} \hspace*{2mm}} \fi%
  \if #9- \else \mbox{(i) \,\, \framebox[8mm]{\rule[-1mm]{0mm}{5mm} \hspace*{-1.6mm} \extext{#9}} \hspace*{2mm}} \fi%
}
\newcommand{\exnum}[9]{%
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}
\newcommand{\exstring}[1]{%
  \mbox{\framebox[0.9\textwidth][l]{\rule[-1mm]{0mm}{5mm} \hspace*{-1.6mm} \extext{#1}} \hspace*{2mm}}%
}

%% new commands
\makeatletter
\newcommand{\ID}[1]{\def\@ID{#1}}
\newcommand{\Date}[1]{\def\@Date{#1}}
\ID{00001}
\Date{YYYY-MM-DD}

%% \exinput{header}

\newcommand{\myID}{\@ID}
\newcommand{\myDate}{\@Date}
\makeatother

%% headings
\markboth{\textnormal{\bf \large Exercicios do R: \myID}}%
{\textnormal{\bf \large Exercicios do R: \myID}}
\pagestyle{myheadings}

\begin{document}

%% title page
\thispagestyle{empty}
{\sf
\textbf{\LARGE{Exercicios do R (\myDate) \hfill Exam ID \myID}}

%\textbf{\large{R exercises for book \myDate \hfill Exam ID \myID}}
\vspace{0.5cm} 

Os exercicios distribuidos aqui fazem parte do conteudo do livro \textbf{Processamento e Modelagem de Dados Financeiros com o R} por Marcelo S. Perlin, disponivel na \href{https://www.amazon.com/Processamento-Modelagem-Dados-Financeiros-Portuguese/dp/8592243513/ref=sr_1_1?ie=UTF8&qid=1486642147&sr=8-1&keywords=Marcelo+perlin}{Amazon}.

\vspace{0.5cm} 

\begin{center}
\includegraphics[width=0.5\linewidth]{CAPADigital_DadosFinanceirosR}
\end{center}

\vspace{0.5cm} 

O conteudo aqui disponibilizado e distribuido com a \href{https://en.wikipedia.org/wiki/MIT_License}{licença do MIT}. 

\vspace*{2cm}

\begin{tabular}{p{14cm}}
\textbf{Nome:} \hrule \\[1.5cm]
\textbf{ID do estudante:} \hrule \\[1.5cm]
\end{tabular}

\newpage

\begin{center}
\LARGE{Respostas}
\end{center}

%% \exinput{questionnaire}
}

\newpage

\begin{enumerate}

%% \exinput{exercises}

\end{enumerate}

\end{document}
