A fish tank initially contains 30 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 x be the amount of salt, in grams, in the fish tank after t minutes have elapsed. Find a formula for the rate of change in the amount of salt, dx/dt, in terms of the amount of salt in the solution and the unknown concentration of incoming brine c. dx dt grams/minute 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 t. x(t) = grams c. In 20 minutes there are 25 grams of salt in the fish tank. What is the concentration of salt in the incoming brine? C = g/L