1. The problem is to understand subtraction, which is taking one number away from another. 2. The formula for subtraction is $a - b = c$, where $a$ is the starting number, $b$ is the number you subtract, and $c$ is the result. 3. Important rules: subtracting zero leaves the number unchanged, and subtracting a number from itself gives zero. 4. Example: $7 - 3 = 4$. Start with 7, take away 3, and you have 4 left. 5. Another example: $10 - 0 = 10$. Taking away zero means the number stays the same. 6. Subtraction is like counting backwards on a number line. 7. Practice: $15 - 5 = 10$, $9 - 4 = 5$, $6 - 6 = 0$. 8. Remember, subtraction is not commutative: $a - b \neq b - a$ in general. 9. So, subtraction helps find the difference between numbers by removing the second number from the first.