Answer:
Option A is the correct choice.
Step-by-step explanation:
We have been given that one building is 15 feet tall and another is 90 feet tall. We are asked to find the height of smaller building proportionally.
Since heights of both buildings are proportional so we will use proportions to find the height of smaller building in terms of height of larger building.

We can see that height of smaller building is 1/6 of the height of larger building, therefore, option A is the correct choice.