At this point of the Earth's surface, the Stratosphere layer is at most at 50 km, and at least at 16 km altitude.
If y represents a height which is in the Stratosphere layer, then we know that y is at least 16 km, which is represented by

,
and y is at most 50 km, which is represented by

.
Combining these 2 inequalities we have:

, where y is in km
The correct answer is 'C'
((-4x^3)(y^4))^-3
--------------------------
(2xy^4)^-4
16x^4y^16
=------------------------
-64x^9y^12
-16y^4
=------------------------
64x^5
-y
=------------------------
4x^5
So the final answer is:
-y^4
-------
4x^5
(Btw if "^" is in front of a number, that means it is an exponent, so when your writing this on paper, just write it as a regular exponent without the "^". I had to do that since I'm on a computer.)
Hopefully this was helpful in some way.