Answer:
It is x2 -4 because it correct
As with any linear equation of this sort, divide by the coefficient of the variable.
.. 470 h = 3008
.. (470 h)/470 = 3008/470
.. h = 3008/470 = 6.4
Because it is BELOW sea level after 10 minutes, it straight away cannot be A) or B), because ascended means going up, so it has to be either C) or D).
I believe the answer is C), as the answer for D) would be -40 meters per minute, but it's still 40. I'm not sure though, so it's either C) or D).