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\begin{equation*}
  \begin{aligned}
    V_1 \frac{d c_1}{dt} &= q (c_2 - c_1) - q_0 c_1 + c_0 u, 
      \qquad c_1 \geq 0, \\
    V_2 \frac{d c_2}{dt} &= q (c_1 - c_2),
      \qquad c_2 \geq 0, \\
    y &= c_2,
  \end{aligned}
\end{equation*}
\end{document}