The scientist was 83.5 feet below sea level while studying ocean life.
Given that:-
Distance the scientist ascended after studying the ocean life = 61.9 feet
Distance below sea level the scientist is after ascending = 21.6 feet
We have to find the distance by which the scientist was below sea level while studying the ocean life.
We know that,
Distance by which the scientist was below sea level while studying the ocean life = Distance the scientist ascended after studying the ocean life + Distance below sea level the scientist is after ascending
Hence, we can write,
Distance by which the scientist was below sea level while studying the ocean life = 61.9 + 21.6 = 83.5 feet.