Enumerating two equations with them having only one reference number

Question

I am currently trying to write a paper. The Format i have to adhere to is for more then one equation:

• that they should have one reference number,
• they need to be enumerated.

I have the easy solution:

\begin{enumerate}
\item 
$ \volST = \BulkM \secoiT \otimes \secoiT : \StrTe $,
\item 
$ \devST = 2\LamesC\ProjT : \epsel. \qquad \textcolor{red}{= \devST^{el}} $
\end{enumerate}

But the output isn´t enumerated, or something like this:

\begin{enumerate}
\item 
\begin{equation}
    \volST = \BulkM \secoiT \otimes \secoiT : \StrTe,
\end{equation}
\item
\begin{equation}
    \devST = 2\LamesC\ProjT : \epsel. \qquad \textcolor{red}{= \devST^{el}}
\end{equation} 
\end{enumerate}

Here is the alignment messed up (wich can be fixed with something like flalign i think?) and i have two numbers indstead of one for both equations. Optimal would be something like an equation environment around the enumerate?

Thanks, Vincent :)

Edit: my solution right now is

\begin{equation} \begin{split}
&\volST = \BulkM \secoiT \otimes \secoiT : \StrTe ,\\
&\devST = 2\LamesC\ProjT : \epsel. \qquad \textcolor{red}{= \devST^{el}}
\end{split} \end{equation} \label{eq}

But i want to reference them like: 1.\ref{eq} or 2.\ref{eq}

Answer 1

Maybe you can use the subequations environment, as Bernard suggested in the comments.

\documentclass{article}
\usepackage{amsmath}
\usepackage{xcolor}
\DeclareMathOperator{\volST}{volST}
\DeclareMathOperator{\BulkM}{BulkM}
\DeclareMathOperator{\secoiT}{secoiT}
\DeclareMathOperator{\StrTe}{StrTe}
\DeclareMathOperator{\devST}{devST}
\DeclareMathOperator{\LamesC}{LamesC}
\DeclareMathOperator{\ProjT}{ProjT}
\DeclareMathOperator{\epsel}{epsel}
\begin{document}
\begin{subequations}
\label{eqs}
\begin{align}
\label{eq1} \volST & = \BulkM \secoiT \otimes \secoiT : \StrTe, \\
\label{eq2} \devST & = 2\LamesC\ProjT : \epsel. \qquad \textcolor{red}{= \devST^{el}}
\end{align}
\end{subequations}

Now you can reference both equations at once with \eqref{eqs}, or reference only equation \eqref{eq1} or \eqref{eq2}.
\end{document}