%% 
%%  \protect \LaTeX  -Referenz, 1. Auf"|lage 2007
%% 
%%  Example 7-6-11 on page 116.
%% 
%%  Copyright (C) 2007 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.
%% 

\documentclass{ttctexa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{355.65944pt}
\setlength\parindent{0pt}
\StartShownPreambleCommands
\usepackage{amsmath,xcolor}
\StopShownPreambleCommands
\begin{document}
\begin{flalign*}
    && \color{red}12(x-1)+20(y-3)+14(z-2) &= 0\\
\text{\color{blue}Ausmultiplizieren und Umstellen ergibt: }
    &&            \boxed{6x+10y+7z-50} &= 0
\end{flalign*}
\end{document}