According to the given data we have the following:
A submarine was 250m below sea level, therefore, that should be in numbers -250 m because is under the water.
It rose 75m.
Therefore, in order to calculate the new depth of the submarine we would have to make the following calculation:
The new depth of the submarine=-250m + 75m
The new depth of the submarine=-175m
Therefore, the new depth of the submarine is -175m