Absolute value is the value of the number, disregarding the sign of the number, so the absolute value of 6 (|6|) is 6 and the absolute value of -6 (|-6|) is also six.
So if we had an equation |-6| + |6| = 6 + 6 = 12, or the absolute value of opposite integers (6 and -6) are added, when we add their absolute values.
The other situation is when you subtract a negative number 6 - (-6) = 6 + 6 = 12, so again the absolute value of opposite integers are added.
The first situation would be the answer if the homework was about absolute values; the second would be the answer if the homework was about adding or subtracting negative numbers.
I hope this helps. John