Hoover Dam on the Colorado River casts a shadow that is 2,904 feet long. At the same time, an 18-foot-tall flagpole next to the dam casts a shadow that is 72 feet long. How tall is the Hoover Dam?

726 feet

Step-by-step explanation:

Object height and shadow length are proportional, so you have ...

(object height) / (shadow length) = (18 ft) / (72 ft) = (dam height) / (2904 ft)

Then the dam height is ...

dam height = (2904 ft) (18/72) = 726 ft

Hoover Dam is 726 feet high.