Equation numbering inside aligned placed next to an alignedat

Something like this?

\documentclass{scrartcl}
\usepackage{amsmath}
\numberwithin{equation}{section}
\begin{document}
\setcounter{section}{1} % just for this example

\noindent
\begin{minipage}{0.25\textwidth} % choose a suitable width
\setlength\abovedisplayskip{0pt}
\setlength\belowdisplayskip{0pt}
\begin{align}
    f_1 &= a + b\\ %1.1 here
    f_2 &= a - b   %1.2 here
\end{align}
\end{minipage}
\hspace{2cm} % or whatever spacing amount is desired
\begin{minipage}{0.6\textwidth}
$\begin{aligned}
    a &= \text{A first line of text}\\
    b &= \text{A second line of text}\\
      &\quad \text{ And a third line}
 \end{aligned}$
\end{minipage}
\end{document}

I don't think this is the best way to set the display.

\documentclass{scrartcl}
\usepackage{amsmath,varwidth}
\usepackage[nopar]{lipsum}

\begin{document}

\lipsum[3]
\begin{center}
\begin{minipage}{0.2\textwidth}% <--- adjust to the needed width
\vspace*{-\baselineskip}
\begin{flalign}
f_1 &= a + b &\\
f_2 &= a - b &
\end{flalign}
\end{minipage}
\qquad
$\begin{aligned}
a &= \text{Some one line text}\\
b &= \begin{varwidth}[t]{0.7\textwidth}
     Some two line text\\
     second line
     \end{varwidth}
\end{aligned}$
\end{center}
\lipsum[4]

\end{document}