A Drug Is Carried into an Organ of Volume

Multiple Choice

A drug is carried into an organ of volume cm³ by a liquid that enters the organ at the rate of p cm³/sec and leaves it at the rate of q cm³/sec. The concentration of the drug in the liquid entering the organ is r g/cm³. If the concentration of the drug in the organ at time is increasing at the rate of ​ ​g/cm³/sec, and the concentration of the drug in the organ initially is g/cm³, find the concentration of the drug in the organ at time .
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