Thales and the Pyramid

Thales (pronounced THAY-lees) is regarded as the father of Greek philosophy and mathematics.
Sometime around the year 600 BC, he visited Egypt to study geometry. There is a legend which says
that Thales impressed the Egyptians by calculating the height of the pyramid at Giza.

A 30 inch stick held vertically from the ground at 3 PM cast a 36 inch shadow,
while at the same time the pyramid cast a shadow 100 feet beyond its base.
At 4 PM, the same stick had a 45 inch shadow, while the pyramid's shadow extended 210 feet beyond its base.

How high was the pyramid?

Answer