Answer:
She must swim 10 feet before she reaches the surface; from level -10 to level 0 (Equation:
)
Explanation:
Based on the information provided, you can assume that the surface of the lake is at level 0.
You know that the swimmer dives 10 feet below the surface; this is the level -10 .
This means that she must swim 10 feet from the level -10 to the level 0 in order to reach the surface of the lake.
Therefore, to find 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:
