Align equations with text before one of them

\documentclass{article}

\usepackage{amsmath}

\begin{document}


zzzzzzzzzzzz

text $\begin{aligned}[b]
   a + b &= c  \\
  d + e &= f 
\end{aligned}$

zzzzzzzzzzzzzzzzzzzzzzzzz

\end{document}

\documentclass{article}
\usepackage{tabstackengine}
\TABstackMath
\begin{document}
text \alignLongstack{a + b =& c\\ d + e =& f} more text
\end{document}

The default baselineskip for a long stack can be set in the preamble with \setstackgap{L}{<length>}.

If it is to be literally used within typeset text, one may wish to add \strutlongstacks{T} to get proper line spacing:

\documentclass{article}
\usepackage{tabstackengine}
\usepackage[nopar]{lipsum}
\strutlongstacks{T}
\TABstackMath
\begin{document}
\lipsum[1]
text \alignLongstack{a + b =& c\\ d + e =& f}
\lipsum[2]
\end{document}