\documentclass{article}
\usepackage{xepersian}
\settextfont{XB Niloofar}
\begin{document}
\begin{equation}
\left\{
\begin{array}{rl}
2x+y+345z&=-3\cr
x-2y&=9\cr
x-2y+7z&=95\cr
\end{array} \right .
\end{equation}
یا
\begin{equation}
\left\{
\begin{array}{llllll}
2x&+y&+345z&=-3\cr
x&-2y&&=9\cr
x&-2y&+7z&=95\cr
\end{array} \right .
\end{equation}
\end{document}