Can someone remind me how to add negative and positive numbers together along with subtracting them correctly? provide examples!

To add a negative and a positive I usually just subtract them so ex: -5+4=-1
and to subtract them I add the numbers together so -5-4=-9 so its basically the opposite   

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.