# How can I vertically center numbering for multi-line equation inside align environment?

In the equation below, +Z_th,kp must stay aligned to the right end of the equal sign, but it seems that I cannot do this without beginning a new line and suppressing its tag. As a result, the numbering becomes aligned to the top as seen here:

How I want the tag to be is like this:

Note that I am using align environment because there is a long derivation and the = sign must stay aligned among all equations. Hence, the solution must maintain the = sign alignment in some fashion. My MWE:

\documentclass[11pt, a4paper]{IEEEtran}

\usepackage{amsmath}
\usepackage{amssymb, amsfonts}

\begin{document}

\begin{align}
\Delta{Z_{lm}} &=  - \frac{(Z_{lk} - Z_{lp})(Z_{km} - Z_{pm})} {Z_{th,kp}- j \frac{d}{y_{b}}}
\\
j \frac{d}{y_{b}} &= \frac{(Z_{lk} - Z_{lp})(Z_{km} - Z_{pm})}{\Delta{Z_{lm}}}
\label{eq:d_yb_find}
\\
&\hphantom{=} + Z_{th,kp}
\notag
\end{align}

\end{document}


\documentclass[11pt, a4paper]{IEEEtran}

\usepackage{amsmath}
\usepackage{amssymb, amsfonts}

\begin{document}

\begin{align}
\Delta{Z_{lm}} &=  - \frac{(Z_{lk} - Z_{lp})(Z_{km} - Z_{pm})} {Z_{th,kp}- j \frac{d}{y_{b}}}
\\
\begin{split}
j \frac{d}{y_{b}} &= \frac{(Z_{lk} - Z_{lp})(Z_{km} - Z_{pm})}{\Delta{Z_{lm}}}
\label{eq:d_yb_find}
\\
&\hphantom{=} + Z_{th,kp}
\end{split}
\end{align}

\end{document}