Answer:
65.7 ft.
Explanation:
at first, let's say she was x fts. below sea level.
over the next 10 minutes she drops 23.5 ft.
that is her height below sea level then becomes
(x + 23.5) ft.
and it's given that she dropped to 89.2 ft. below sea level.
x + 23.5 = 89.2
x = 89.2 - 23.5
x = 65.7 ft.
and x was the height she's been below sea level.
Therefore ,she's been 65.7 ft. below sea level.