$\frac{dA}{dt} = C_1Q_1 + C_2Q_2 - \frac{A}{V(t)}Q_{out}$

$\frac{dA}{dt} = C_1Q_1 + C_2Q_2 - A Q_{out}$

$\frac{dA}{dt} = C_1Q_1 + C_2Q_2 + \frac{A}{V(t)}Q_{out}$

$\frac{dA}{dt} = (C_1+C_2)(Q_1+Q_2) - \frac{A}{V}Q_{out}$