1. **State the problem:** Calculate the sum of 6 and 7. 2. **Formula used:** Addition of two numbers is given by $a + b$. 3. **Apply the formula:** Here, $a = 6$ and $b = 7$, so we calculate $6 + 7$. 4. **Perform the addition:** $6 + 7 = 13$. 5. **Final answer:** The sum of 6 and 7 is **13**.