Provide examples to the following: the associative property of addition holds true for negative intergers

I think you just need examples, and not to prove that it is true ...

For positive integers, we might do:

3 + (4 + 5) = (3+4) + 5

3 + 9 = 7 + 12

For negative integers we could do:

-3 + (-2 + - 1) = (-3 + - 2) + - 1

-3 + - 3 = - 5 + - 1

-6 = - 6