Two tanks are interconnected. Tank A contains 60 grams of salt in 30 liters of water, and Tank B contains 70 grams of salt in 20 liters of water. A solution of 2 gram/L flows into Tank A at a rate of 7 L/min, while a solution of 4 grams/L flows into Tank B at a rate of 8 L/min. The tanks are well mixed. The tanks are connected, so 9 L/min flows from Tank A to Tank B, while 2 L/min flows from Tank B to Tank A. An additional 15 L/min drains from Tank B. Letting x represent the grams of salt in Tank A, and y represent the grams of salt in Tank B, set up the system of differential equations for these two tanks.