Geometry Review Exam Help!!!!!!

A tree is standing next to a 40 foot high building. the tree has an 18 foot shadow, while the building has a 16 fooot shadow. How tall is the tree, rounded to the nearest foot.\

A. 45 ft
B. 36 ft
C. 13 Ft
D. 7 Ft

set up as a proportion:
40/16=x/18 where x is the height of the tree and solve.
A: 45ft

Proportions
Let h = the height
Height of building / the length its shadow = 40/16 = h/18
18(40) = h(16)
720 = 16h
45 ft = h