8th grade math
posted by liz on .
if a person is 6 feet tall and casts a 9 foot shadow, how tall would the shadow of a 100 foot tall tree be?

6 / 9 = 100 / x Multiply both sides with x
6 x / 9 = 100 Multiply both sides with 9
6 x = 9 * 100
6 x = 900 Divide both sides with 6ΕΎ
x = 900 / 6
x = 150 ft
OR
9 / 6 = 1.5
x / 100 = 1.5 Multiply both sides with 100
x = 1.5 * 100
x = 150 ft 
or using proportions and cross multiply:
6:9
100:?
? = 100*9/6=150 
A tree and a building stand side by side. The 5foot tall tree casts a shadow of 12 feet. If the building is 80 feet tall, how long is its shadow?