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 ft and its height when built was 481 ft. (It was the tallest man made structure in the world for more than 3800 years.) The density of the limestone is about 150 lb/ft³.
(a) Estimate the total work done in building the pyramid.
(b) If each laborer worked 10 hours a day for 20 years, for 340 days a year, and did 200 ft-lb/h of work in lifting the limestone blocks into place, about how many laborers were needed to construct the pyramid?