An elliptical artificial island is required for a reclamation project. The major axis of the ellipse is 10 km and the minor axis is 7.5 km (Figure P4.23). A rock breakwater, 100 m thick, forms the edges of the island. The area within the breakwater is to be filled with sand. The sand in its loosest state has a porosity of 90% and the desired porosity, when compacted, is 20%. Assuming the average thickness of the completed island is 100 m, determine the quantity of sand required.