\documentclass[12pt,twoside]{article}
\usepackage{amsthm,amssymb,amsmath,amsfonts}
\begin{document}
	\begin{equation}
	\left\lbrace \begin{array}{lc}
	Min    I_{j}=\sum\limits_{k=1}^4 \omega_{k}I_{k}\\
	St     M_{s}-1.6\leq 0 \\
          j_{5}\leq0.9 \\
	\end{array}\right
	\end{equation}
\end{document}