To help Susie understand why \( 7 - (-3) \) equals \( 10 \) using a number line model, the best response is:
On a number line, start at point \(-3\). Then move \(7\) in the positive direction.
Here's the reasoning:
- Starting at \(-3\) means you're at the position of the negative number.
- When you subtract a negative number, it is equivalent to adding the positive version of that number. So moving \(7\) units in the positive direction from \(-3\) would lead you to \(7\).
- Thus, starting from \(-3\) and moving \(7\) units to the right will lead you to the point \(10\), which clearly illustrates that \(7 - (-3) = 10\).
This way, Susie can visualize and understand that subtracting a negative number effectively increases the value, which is why her answer is greater than either of the original numbers.