numbering a several line "equation"

Question

I'm trying to number an equation, which spans over several lines. I need for it to look like this

My current tex for this is:

\documentclass[a4paper,12pt]{article}

\begin{center}
 {\it ``If A is true, then B is true\\
  A is true \\ 
  \line(1,0){140}
  \\Therefore, B is true''}
\end{center}

Answer 1

\documentclass[a4paper,12pt]{article}
\begin{document}
\begin{equation}
 \begin{tabular}{c}
  ``If  $A$ is true, then $B$ is true\\
  $A$ is true \\\hline
  Therefore, $B$ is true''
  \end{tabular}
\end{equation}
\end{document}