140 feet descent in 14 hours, mean:
140/14 = 10 feet/hour [descend rate]
From - 140 feet to -284.6 feet, it is:
[tex]284.6-140=144.6[/tex]At 10 feet/hour, it will take:
144.6/10 = 14.46 hours
Presuming the question asks for how long (total time) the submarine is descending, we can add both descend times:
14 hours + 14.46 = 28.46 hours
Answer:
28.46 hours