A large aquarium should contain 10,000 liters of water when it is filled correctly. It will overflow if it gets up to 12,000 lit
ers. The fish will get sick if it gets down to 4,000 liters. The aquarium has an automatic system to help keep the correct water level. If the water level is too low, a faucet fills it. If the water level is too high, a drain opens. One day, the system stops working correctly. The faucet starts to fill the aquarium at a rate of 30 liters per minute, and the drain opens at the same time, draining the water at a rate of 20 liters per minute. How long will it take until the tank starts overflowing or the fish get sick (if it started with 10,000 liters of water)?
