Final answer:
The scientist must ascend 77.1 feet to get back to sea level.
Step-by-step explanation:
To find the number of feet the scientist must ascend to get back to sea level, we need to first calculate the total change in elevation.
The scientist descends 31.6 feet and then ascends 19.2 feet, resulting in a net change of 31.6 - 19.2 = 12.4 feet below sea level.
Next, the scientist descends an additional 89.5 feet, bringing the total change in elevation to 12.4 - 89.5 = -77.1 feet below sea level.
Since the scientist wants to return to sea level, she must ascend 77.1 feet.