For this problem, you could use the Scale Factor.
I will use x for the height of the building.
So 8 is to 90 as 5 is to x.
Our equation is:
8(SF) = 90
Divide both side by 8:
SF = 45/4
Then, we plug SF into the next equation:
5(SF) = x
5(45/4) = x
56.25 = x
Round to the nearest foot, and the height of the building is 56 feet.