Answer: Choice C
7 + (-10) = -3
Note that the result is negative, and not positive. I'm assuming your teacher made a typo.
The negative 3 is because the upper arrow is in the negative region, to the left of the 0.
The lower arrow represents 7 since we start at 0 and move 7 units to the right.
The upper arrow represents -10 to indicate we move 10 units to the left.
We can think of 7+(-10) as 7-10 and that is the same as -10+7. To evaluate this without a number line, we can subtract 10-7 to get 3, but the result is negative because the 10 is larger and it is negative. It's like having 10 iou's and you pay off 7 dollars of debt. That means you're still 3 dollars in debt, which is represented by -3.
