Answer:
The opposite of Carlos's elevation would be +12ft.
Explanation:
This question is using positive and negative integers to represent elevation and descending. The surface of the pool would represent an elevation of 0, where we are level. However, when Carlos descends (swims to the bottom) of the pool, he is at an elevation of -12 because he is below the surface. The opposite of -12 would be +12. So the opposite of where Carlos is -12ft below the surface of the water would be +12 foot above the surface of the water.