On a sunny day, the length of the shadow on the ground from a person 1.8 m tall is 90 cm

On a sunny day, the length of the shadow on the ground from a person 1.8 m tall is 90 cm, and from a tree 10 m. What is the height of the tree?

This problem can be solved by the proportion:
The ratio of the shadow from the subject to the height of the subject
90 cm = 0.9 m
0.9 m / 1.8 m = 10 m / xm
The product of the extreme terms is equal to the product of the means, then:
0.9x = 1.8 * 10
0.9x = 18
x = 20 (m)
Answer: 20 m