6. A tank has pure water flowing into it at 12 liters per minute. The contents of the tank are kept thoroughly mixed, and the contents flow out at 10 liters per minute. Initially, the tank contains 10 kg of salt in 100 liters of water. How much salt will there be in the tank after 30 minutes? (Hint: The inflow rate is greater than the outflow rate.) (2 points) Sol: Let X be the amount of salt in the tank at any time t. The volume V of liquid in the tank is V= of salt after t minutes is then = V after t minutes. The concentration and the rate of change of X is ' dx dt = And thus X(t)= X(30)=