Negative 6 plus positive 6 equals what?

The answer is 0.

-6 + 6 = 0. It takes the sign of the greater number. Since the numbers are equal it becomes neither. 0 is neither a positive nor negative number.

For another example if the problem was -6 + 10, Since 10 is the greater number your answer will be positive. 10 - 6 = 4. (Just change the positive + sign to the negative - sign).