The city worker descends 3 meters underground level, which means -3 units setting the initial place at 0.
Then, she descends 4 more meters underground, she is located -3meters and then descends -4 more meters.
So the worker is -4-3 = -7 meters from ground level, which means he is underground.
The corrects true statements are:
The worker is -7 meters from ground level,
One of the addends is -3.