Answer:
(a)

(b)

(c)

Step-by-step explanation:
Given
See attachment for complete question
Solving (a): The elevation at the surface level:
Let x represents the elevation
At the surface level, the elevation is 0.
So:

Solving (b): Swim down 300ft:
A downward movement will be represented as negative.
So, the new elevation is:

Where
--- previous value of x

This implies that:


The new elevation is -300ft
Solving (c): Swim down 150ft:
A downward movement will be represented as negative.
So, the new elevation is:

Where
--- previous value of x

This implies that:


The new elevation is -450ft