tree's height     person's height
-------------  =  ---------------
tree's shadow     person's shadow

This has some unnecessary information.  It was put in to see if you would try to
use it in solving the problem.  But it doesn't matter whether you're 80 feet or
100 feet or 73 feet or 29 feet from the base of a tree!  The lengths of the
shadows of the man and the tree aren't going to change because he moves nearer
to or farther from the tree!  So "80 feet" is unnecessary information and must
be ignored.   

 

"IS TO" means "OVER" and "AS" means "EQUALS".

So, 



So,



So,



So we cross multiply:





We divide both sides by 6



We reduce the fraction by dividing top and bottom by 2



Change to a mixed number:



Edwin