\documentclass[a4paper]{article}
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\begin{document}
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\parbox{.7\linewidth}{
\begin{align}
  13 \cdot (4a - 3)^2 &= 13 \cdot (16a^2 - 24a + 9) \\
                      &= 208a^2 - 312a + 117
\end{align}
}

\end{document}
