1. **State the problem:** Calculate the sum of 12 and 20. 2. **Formula used:** Addition of two numbers is given by $a + b$. 3. **Apply the formula:** Here, $a = 12$ and $b = 20$, so we calculate: $$12 + 20$$ 4. **Perform the addition:** $$12 + 20 = 32$$ 5. **Final answer:** The sum of 12 and 20 is 32.