Consider three compartments of the body (see figure): Circulatory system ( C, with volume Ve ), digestive system (D, with volume Vs ), and urinary system ( U, with volume Vu ). Consider two substances A and B. Concentrations of these substances (grams/L) in the compartments are [A]c,[A]d, and [A]u and [B]c,[B]d, and [B]u respectively. Substance A is inputted into the circulatory system at a rate of Ain,e grams per minute (may be through the respiratory system that is not included here). B is obtained through digestion at a rate of Bin,d grams/min. Substance A can be transported back and forth (from the compartment with the higher concentration to the compartment with lower concentration) between the circulatory and digestive systems at a net rate of k1[A] grams/min where refers to the difference in the concentrations (similarly to the diffusion process). A is excreted from the circulatory system to the urinary system at a rate of k2[Ac] grams/min. Substance B is similarly exchanged back and forth between the circulatory and digestive systems at a net rate of k3[B] grams/min. B is consumed in the circulatory system at a rate of k4[Bc]grams/min. B is also diverted from the digestive system to the urinary system at a rate of ks[Bd]grams/min. Both substances are excreted by the urinary system at a rate of k6[Av] and k6[Bu] grams/min, respectively. Reactions are shown schematically in the attached diagram. For simplicity, assume that volumes do not change as part of the exchange reactions