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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def C_stock(self):
 """Return the required concentration of material in the stock given a reactor's desired system flow rate, system concentration, and stock flow rate. :return: Concentration of material in the stock :rtype: float """

        return self._C_sys * (self._Q_sys / self._Q_stock).to(u.dimensionless)