1. The problem is to understand the formula for the sum of two variables $a$ and $b$. 2. The formula for the sum is simply: $$a + b$$ 3. This formula means you add the value of $a$ to the value of $b$. 4. Important rules: - Addition is commutative: $a + b = b + a$ - Addition is associative: $(a + b) + c = a + (b + c)$ 5. Example: If $a = 3$ and $b = 5$, then $$a + b = 3 + 5 = 8$$ 6. So, the sum of $a$ and $b$ is the total amount when you combine both values.