2024 DMC Mock 10 Problems/Problem 7

The Reunion Tower is originally $20\%$ of the height of the Burj Khalifa, so to make it $90\%$ of the height we need to scale it by $\frac{9}{2}$ . This scales the area by $\frac{81}{4}$ , so the answer is $100\cdot\frac{81}{4}=\boxed{2025}$ .