1. Let's state the problem: Find the sum of 345 and 678. 2. The formula for addition is straightforward: $a + b = c$, where $a$ and $b$ are numbers and $c$ is their sum. 3. Add the numbers step-by-step: - Add the units digits: $5 + 8 = 13$, write 3 and carry over 1. - Add the tens digits plus carry: $4 + 7 + 1 = 12$, write 2 and carry over 1. - Add the hundreds digits plus carry: $3 + 6 + 1 = 10$, write 0 and carry over 1. - Since there is a carry over 1, write it as the new thousand's digit. 4. So, the sum is $1023$. 5. Therefore, $345 + 678 = 1023$. This is a typical Grade 6 level addition problem in Kenya.