1. **State the problem:** Calculate the sum of 1234 and 123. 2. **Formula used:** Addition of two numbers is given by $$a + b$$ where $a=1234$ and $b=123$. 3. **Perform the addition:** $$1234 + 123 = 1357$$ 4. **Explanation:** Adding 123 to 1234 means increasing 1234 by 123 units, resulting in 1357. 5. **Final answer:** $$1357$$