A fish tank initially contains 40 liters of pure water. Brine of constant, but unknown, concentration of salt is flowing in at 4 liters per minute. The solution is mixed well and drained at 4 liters per minute. a. Let a: be the amount of salt, in grams, in the fish tank after 15 minutes have elapsed. Find a formula for the rate of change in the amount of salt, doc/alt, in terms of the amount of salt in the solution as and the unknown concentration of incoming brine 6. dx C] rams/minute dt _ g b. Find a formula for the amount of salt, in grams, after t minutes have elapsed. Your answer should be in terms of c and 75. 53(75) = C] grams c. In 35 minutes there are 20 grams of salt in the fish tank. What is the concentration of salt in the incoming brine? CIDg/L