The Great Pyramid of King Khufu was built of limestone in Egypt over a 20-year time period from 2580 BC to 2560 BC. Its base is a square with side length 756 feet and its height when built was 481 feet. (It was the tallest man-made structure in the world for more than 3800 years.) The density of the limestone is about 150 pounds per cubic feet. Estimate the total work done in building the pyramid, in Newtons. You will want to begin by converting your units.