Question

A 6-foot spruce tree is planted 15 feet from a lighted streetlight whose lamp is 18 feet above the ground. How many feet long is the shadow of that tree?

Answer 1

draw the picture to get

Answer 2

the two triangles are similar, so you can set up the proportion

18/6 = (15+x)/x

and cross multiply to get

18x = 6(15+x)

from here, you solve for x to get the length of the tree's shadow