Answer:

So then the model would have 10 inches.
Explanation:
For this case we know that the actual building measures 900 ft
And we have the following ratio between the scale model and the real structure 3.5 in = 225 ft.
So we can use the following proportion:

Where x represent the height of the model at inches. And solving for x we got:

So then the model would have 10 inches.