コード

\documentclass[uplatex,dvipdfmx,12pt]{article}

\usepackage{hyperref}
\usepackage{hyperref}
\hypersetup{
  colorlinks,citecolor=blue,filecolor=blue,linkcolor=blue,urlcolor=blue
  }

\newcounter{mycount}

\newcommand{\qn}[1]{
  \subsubsection*{
  \label{sec:qn\thesection\alph{mycount}}
  \hyperref[sec:an\thesection\alph{mycount}]{\thesection\alph{mycount}\quad\textit{#1}}
  \stepcounter{mycount}}
  }

\newcommand{\an}{
  \subsubsection*{
  \label{sec:an\thesection\alph{mycount}}
  \hyperref[sec:qn\thesection\alph{mycount}]{\thesection\alph{mycount}}
  \stepcounter{mycount}}
  }



\begin{document}
\tableofcontents

\section{Test} \setcounter{mycount}{1}
  \qn{Test problem}
  Something.

  \qn{}
  Something.

  

\addcontentsline{toc}{subsection}{Answers and Hints}
\subsection*{Answers and Hints} \setcounter{mycount}{1}
  \an
  The answer of the first question.

  \an
  The answer of the second question.

\end{document}

出力例

「1a Test problem」を押すと答えの「1a」に、「1a」を押すと「1a Test problem」に飛ぶようになっています。