Answer:
-9 + (-9) = -18
Step-by-step explanation:
They start on -9 and end on -18. That means -9 has to be an addend and -18 is the sum.
-18 - (-9) = -18 + 9 = -9, which means the other addend is also -9.
Hope this helps!
(Also I don't think you need to add the parenthesis in the box.)
