Answer: Choice D which is -(-6 + 17) = 6 + (-17)
A sum is the result of adding two numbers. It doesn't matter if those numbers are positive or negative. In choice D, we start with -6 and 17 which add to -6+17. Then we apply a negative sign to that entire thing to take the complete opposite to get -(-6+17)
The negative sign is distributed through to each term. Whatever was negative turns positive, or vice versa. So -6 turns to +6 or just 6, and 17 becomes -17. That explains how your teacher got 6 + (-17).
