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 (see figure).  A rock breakwater, 100 m thick, forms the edges of the island. The area  within the breakwater is to be filled with sand. Sand in its loosest state has  a porosity of 90 percent and desired porosity, when compacted, is 20%.  Assuming average thickness of the completed island is 100 m, determine  the quantity of sand required.

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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 (see figure). 
A rock breakwater, 100 m thick, forms the edges of the island. The area 
within the breakwater is to be filled with sand. Sand in its loosest state has 
a porosity of 90 percent and desired porosity, when compacted, is 20%. 
Assuming average thickness of the completed island is 100 m, determine 
the quantity of sand required.