\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
\pagestyle{empty}
\begin{document}
\begin{equation*}
  \aligned 
    A &= \begin{bmatrix}
          0 & 0 & 0 & 1 & 0 & 0 \\
          0 & 0 & 0 & 0 & 1 & 0 \\
          0 & 0 & 0 & 0 & 0 & 1 \\
          0 & 0 & -g & -c/m & 0 & 0 \\
          0 & 0 & 0 & 0 & -c/m & 0 \\
          0 & 0 & 0 & 0 & 0 & 0
        \end{bmatrix}, &\qquad 
    B &= \begin{bmatrix}
          0 & 0 \\ 0 & 0 \\ 0 & 0 \\ 1/m & 0 \\ 0 & 1/m \\ r/J & 0 
	\end{bmatrix}, \\[1ex]
    C &= \begin{bmatrix}
	  1 & 0 & 0 & 0 & 0 & 0 \\
	  0 & 1 & 0 & 0 & 0 & 0
        \end{bmatrix}, &\qquad
    D &= \begin{bmatrix}0 & 0 \\ 0 & 0 \end{bmatrix}.
  \endaligned
\end{equation*}
\end{document}