4) A barge of mass of 15000 kg, made from a metal with a density of 7500 kg/m³, is being loaded with in a closed dock of a surface area of 6633 m2 with ore of 3 g/cm³. When 80,000 kg of ore are aboard, the barge sinks. How does the water level in the dock alter? You may assume the area of the barge is negligible in comparison with the area of the dock.