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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 Q_stock(self):
 """Return the required flow rate from the stock of material given a reactor's desired system flow rate, system concentration, and stock concentration. :return: Flow rate from the stock of material :rtype: float """

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