Use similar triangles to solve. a person who is 5 feet tall is standing 140 ft from the base of a tree and the tree cast a 154 foot shadow. the person's shadow is 14 ft in length what is the height of the tree

For this case we have the following relationship using similarity of triangles:
 (x / 154) = (5/14)
 Clearing the value of x we have:
 x = (5/14) * (154)
 Rewriting we have:
 x = 55 feet
 
 the height of the tree is:
 x = 55 feet

What’s the equation you are trying to solve to get x?