\listfiles
\documentclass{jarticle}
\usepackage{amsmath}
\usepackage{array}
\begin{document}

\[
\begin{array}{r @{{}={}} c @{{}+{}} l}
    a & \underbrace{b + c} & e + f\\
      & d                  & e + f.
\end{array}
\]

\end{document}
