%% 
%%  An UIT Edition example
%% 
%%  Example 06-20-1 on page 123.
%% 
%%  Copyright (C) 2010 Herbert Voss
%% 
%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
%% 
%%  See http://www.latex-project.org/lppl.txt for details.
%% 
%% 
%% ==== 
% Show page(s) 1
%% 
\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{375.57637pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\StartShownPreambleCommands
\usepackage{amsmath,calc}
\StopShownPreambleCommands
\begin{document}
\setlength\fboxsep{0pt}
\setlength\abovedisplayskip{10pt}\setlength\belowdisplayskip{10pt}
\fbox{\parbox{\linewidth}{\setlength\fboxsep{5pt}%
\begin{xalignat*}{2}
\framebox[0.125\columnwidth]{xalignat} &= \framebox[0.125\columnwidth]{x} & \framebox[0.125\columnwidth]{x} &= \framebox[0.125\columnwidth]{x}\\
\framebox[0.125\columnwidth]{xalignat} &= \framebox[0.1\columnwidth]{x} & \framebox[0.1\columnwidth]{x} &= \framebox[0.1\columnwidth]{x}
\end{xalignat*}}}
\end{document}