Answer: 59 feet
Explanation:
First the sea turtle descended 28 feet.
It then ascends 5 feet which means it is now:
= 28 - 5
= 23 feet below surface
It then descends 9 feet and repeats that descent 4 time:
= 9 * 4
= 36 feet below the surface
Total distance below the surface:
= 23 + 36
= 59 feet