\documentclass[a4paper]{article}

\usepackage{a4wide,color,Sweave,url,amsmath,booktabs,longtable}
\newenvironment{question}{\item \textbf{Problem}\newline}{}
\newenvironment{solution}{\textbf{Solution}\newline}{}
\newenvironment{answerlist}{\renewcommand{\labelenumi}{(\alph{enumi})}\begin{enumerate}}{\end{enumerate}}

\begin{document}
\begin{enumerate}
%% \exinput{exercises}
\end{enumerate}
\end{document}
