Answer: 12.5 ft
If we are assuming these triangles to be similar, 15, the tree's shadow, is similar to 6, the person's shadow because corresponding lengths of similar triangles are similar. From this, we get 15/6. We also know that h, the tree, is similar to the person, who is 5 feet tall. So then we get h/5. It does not matter whether you do h/5 or 5/h but corresponding lengths have to either both be the denominators or numerators. If I were to do 5/h, I would have 6/15 and not 15/6.
Explanation:
You start by creating a proportion:
15/6 = h/5
Cross multiply
75 = 6h
Divide 6 on each side
12.5 = h