\documentclass{article}

\usepackage{amsmath}

\begin{document}

\begin{align*}
  %N &= (-9) - (+5) &
  %O &= (+7) - (-8) &
  %P &= (+5) + (-6) &
  %Q &= (-3) + (+2) \\
  N &= \underbrace{\underbrace{(-9)}_{-9} \!\underbrace{{}- (+5)}_{{}-5}}_{-14} &
  O &= \underbrace{\underbrace{(+7)}_{ 7} \!\underbrace{{}- (-8)}_{{}+8}}_{ 15} &
  P &= \underbrace{\underbrace{(+5)}_{ 5} \!\underbrace{{}+ (-6)}_{{}-6}}_{- 1} &
  Q &= \underbrace{\underbrace{(-3)}_{-3} \!\underbrace{{}+ (+2)}_{{}+2}}_{- 1}
\end{align*}

\end{document}