Answer: The new depth of submarines would be -195 meters, i.e. 195 meters below the sea level.
Explanation:
Since we have given that
Depth of submarine = 250 meters below sea level. = (-) 250 meters
Rises by = 75 meters = (+) 75 meters
Dives by = 20 meters = (-) 20 meters
So, the new depth would be

Hence, the new depth of submarines would be -195 meters, i.e. 195 meters below the sea level.