Question 750067
Similar triangles
if you consider the tree and the rod as
one ratio and the tree's shadow and the 
rod's shadow as the other ratio.
Then you have:
x/9 = 18/6  (x being the tree)
The sides must match like for like
Cross multiply:
6x = 162
Divide both sides by 6

x = 27
Therefore the tree is 27 feet tall.
:-)