Answer :
There are two statements here, showing quantities in real world which are additive inverse of each other :
2. Noa hiked 2 mi up a mountain trail and then hiked 2 mi down the trail.
here, we can depict going up as +2 miles and going down the trail as -2
4. A hot-air balloon ascends 2000 ft from the ground and then descends 2000 ft.
And here we can assume going up the ground aa + 2000 ft and going down aa - 2000 ft .