Align equations within one line

Question

I would like to align multiple equations (with one rather long one) within one line of my document with \begin{align}. But using "&" for spacing causes rather too long spaces and weird right alignment for some parts. It causes my equation enumeration in the document to be placed in the next empty line. I am using amsmath with the fleqn option.

I hope my problem gets clearer with my code: Many thanks in advance.

\documentclass[]{scrbook}
\usepackage[fleqn]{amsmath}
\usepackage{amssymb}

\begin{document}
{\setlength{\mathindent}{0cm}

\begin{subequations}\label{eq:MINLP}

   \begin{align}
     \mathrm{min} \quad &\sum_{j=1}^{NE}(y_{j}-V_{1,j})^{2} 
     \tag{\ref{eq:MINLP}}\\

     \mathrm{s.t.} \quad & f_{j,k}(V_{n,j},V_{2n,j},V_{2n+1,j}) \le
     M_{n,j,k}^{up}(1-\delta_{n,k}) && n \,  \epsilon \, \mathcal{N}_{b},\,
     k \,  \epsilon \,  \mathcal{F},\, j \,  \epsilon  \, \mathcal{E} \\

     & f_{j,k}(V_{n,j},V_{2n,j},V_{2n+1,j}) \ge M_{n,j,k}^{lo}
    (1-\delta_{n,k}) && n=a+b \\

   \end{align}
\end{subequations}}
\end{document}

I would like to push the part starting with "n..." further to the left but still be aligned, such that the equation enumeration 3.1a will be in the same line.

Answer 1

The posted code does not have the spacing shown, but generates errors due to the blank lines, this version runs without error

\documentclass[]{scrbook}
\usepackage[fleqn]{amsmath}
\usepackage{amssymb}

\begin{document}
%\setlength{\mathindent}{0cm}

\begin{subequations}\label{eq:MINLP}

   \begin{align}
     \min &\sum_{j=1}^{NE}(y_{j}-V_{1,j})^{2} 
     \tag{\ref{eq:MINLP}}\\
     \mathrm{s.t.} \quad & f_{j,k}(V_{n,j},V_{2n,j},V_{2n+1,j}) \le
     M_{n,j,k}^{\mathrm{up}}(1-\delta_{n,k}) && n \in \mathcal{N}_{b},\,
     k \in  \mathcal{F},\, j \in \mathcal{E} \\
     & f_{j,k}(V_{n,j},V_{2n,j},V_{2n+1,j}) \ge M_{n,j,k}^{\mathrm{lo}}
    (1-\delta_{n,k}) && n=a+b 
   \end{align}
\end{subequations}
\end{document}