A fish tank initially contains 10 liters of pure water. Brine of constant, but unknown, concentration of salt is flowing in at 2 liters per minute. The solution is mixed well and drained at 2 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 x 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 40 minutes there are 20 grams of salt in the fish tank. What is the concentration of salt in the incoming brine? c=________________________g/L Any help would be greatly appreciated.