Answer:
If I'm not mistaken the height should be 18 ft.
Explanation:
I get this because the base line of the human is 13 ft and the base line of the building is 39 ft. In order to get from 13 to 39 you would have to multiply 13, 3 times. Which means you would also have to take the height line of the human and multiply it by 3 to get 18.
Hope this helps :)