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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 rpm(self, vol_per_rev):
 """Return the pump speed required for the reactor's stock of material given the volume of fluid output per revolution by the stock's pump. :param vol_per_rev: Volume of fluid pumped per revolution (dependent on pump and tubing) :type vol_per_rev: float :return: Pump speed for the material stock, in revolutions per minute :rtype: float """

        return Stock.rpm(self, vol_per_rev, self.Q_stock()).to(u.rev/u.min)