The answer is -8.
Try switching the signs at first. For example : -12 + 4 would become 12 - 4 and the answer to that would be 8, then switch the signs back and you would get -8. Not sure if that works 100% of the time but it helped me until I had it down.
-12 +4 = -8.
-12, -11 (+1), -10 (+2), -9 (+3), -8(+4).
Hope this helps.
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