this is high school calculus

and i have no idea how to do this

question:

It is reported that the Great Pyramid of Egypt was built in 20 years.

A side of its square has measures 755 feet, and its height is 410 feet.

The stone making up the Pyrimid has a density of approximately 200 pounds per cubic foot.

Assume that a typical worker lifted ten 50-pounds blocks a distance of 4 feet every hour and that he worked 10 hours a day,

300 days a year. Estimate how many workers were needed to build the Great Pyrimid of Egypt.

the answer is around xx,000 people

thx!