Question

A lamppost casts a shadow of that is 15 yards long. A 3-foot-tall mailbox casts a shadow that is 5 yards long. How tall is the lamppost?

Answer 1

1/5 = x/15 solve for x
15 * 1/5 = 15/5 = 3
it is 3 yards tall

(I changed the 3 feet to 1 yard to keep the units the same)

Answer 2

Use the proportion x/15 = 3/5 (height of object/length of shadow) and cross multiply. 5x = 45. divide both sides by three and x=9.