% asd worksheet template
\documentclass[border = 1mm]{standalone}
\usepackage{dcolumn}
    
\newcolumntype{d}[1]{cD{.}{.}{#1}}

% modify values 
\def\addsub{-} 
\def\deca{70.256}
\def\decb{16.362}
\def\answer{53.894}


\begin{document}
\begin{tabular}{d{2.3}}
    &\deca \tabularnewline
    $\addsub$&\decb \tabularnewline
    \hline
    &\answer \tabularnewline
    \hline
\end{tabular}
\end{document}
