Answer :
In step 4, -9 is added to 9 to make 0.
This is an example of the inverse property of addition. -9 and 9 are inverses, and when inverses are added together they cancel out and equal 0.
(by the way, since you know it involves addition and there's only one answer choice which does, it has to be that one)
This is an example of the inverse property of addition. -9 and 9 are inverses, and when inverses are added together they cancel out and equal 0.
(by the way, since you know it involves addition and there's only one answer choice which does, it has to be that one)