1. **State the problem:** We need to find the sum of 9000 and 9000. 2. **Formula used:** Addition of two numbers is given by $$a + b$$ where $a$ and $b$ are the numbers. 3. **Apply the formula:** Here, $a = 9000$ and $b = 9000$. 4. **Calculate:** $$9000 + 9000 = 18000$$ 5. **Conclusion:** The sum of 9000 and 9000 is 18000.