Answer:
The swimmer must swim 10 feet before she reaches the surface; from level -10 to level 0 (The equation is: [tex]-10+10=0[/tex])
Step-by-step explanation:
We can assume that the surface of the lake is at level 0.
The swimmer dives 10 feet below the surface; then this is the level -10.
This means that the swimmer must swim 10 feet from the level -10 to the level 0 in order to reach the surface of the lake.
Therefore, in order to calculate how far she must swim before she reaches the surface, it is necessary to add levels -10 and +10 to get the level 0.
This can be represented with the following equation:
[tex]-10+10=0[/tex]
