A 1,000-liter tank initially contains 200 liters of brine containing 100 kg of salt. Brine containing 1 kg of salt per liter enters the tank at the rate of 5 liters/ sec, and the mixture kept uniform by stirring is pumped out at the rate of 4 liters/sec. How much salt is in the tank when it is full of brine?

A 1,000-liter tank initially contains 200 liters of brine containing 100 kg of salt. Brine containing 1 kg of salt per liter enters the tank at the rate of 5 liters/ sec, and the mixture kept uniform by stirring is pumped out at the rate of 4 liters/sec. How much salt is in the tank when it is full of brine?