Answer:
First, in standard notation, we must define our zero.
In this case, would make sense to define the zero in the surface of the water.
(below is a number line so you can see the process to think this)
Then if the whale is swimming 60ft bellow the surface of the water, then the first position of the whale is:
-60
Now the whale goes up 30ft, then the new position of the whale is:
-60ft + 30ft = -30ft.
The correct option is A:
The equation is -60 + 30 = -30. The whale is 30 feet below the water's surface.
(you wrote that the equation was equal to +30 instead of -30 in the option A, i supposed that it was a typo)
