There are many answers we could go with here. One such answer could be the following:
You are 6 meters below the ocean surface doing a deep sea dive. This is represented by -6. Then going up 6 meters means you'll add on 6 to say (-6)+6 = 0, showing that you are at the 0 meter height, aka sea level.
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Another possible answer could be this:
You are 6 dollars in debt. Debt is represented with negative numbers. You then somehow get 6 dollars in which you use to pay off that debt. Your balance is now (-6) + 6 = 0 dollars.
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Another possible answer could be this:
Walking to the left is defined as moving in a negative direction. So -6 could mean we've moved 6 feet to the left. On the flip side, +6 means we move 6 feet to the right. The two cancel each other out (-6)+6 = 0 which says at the end of the day, we haven't moved anywhere. In other words, our displacement is 0 feet.
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I'm sure there are other more creative ways to answer this question, but those three ideas above are good possible starting points.