\documentclass[a4paper]{book}
\RequirePackage{amsthm}
\RequirePackage{amssymb}
\RequirePackage{amsmath}
\usepackage{empheq} % autoload amsmath
\usepackage{xepersian}


\begin{document}
\begin{empheq}[left={x=}\empheqlbrace]{align}
  & a + b \\
  & c + d \label{eq:b}\\
  & e + f
\end{empheq}
%

Total group: \eqref{eq:tot}, just one: \eqref{eq:b}

\begin{subequations}
\begin{empheq}[left={(LS1)}\empheqlbrace]{align} \label{eq:1.2}
& H_k v + \nabla f (x_k) + \sum\limits_{i=1}^m \lambda_i \nabla g_i (x_k) = 0  \tag{111}\\
& \mu_{k,i} \big\langle \nabla g_i (x_k) , v \big\rangle + \lambda_i g_i (x_k) = 0 \qquad i = 1, \ldots, m \tag{222} 
\end{empheq}
\end{subequations} 
\eqref{eq:1.2}
\end{document}
Samani