C, I’m pretty sure
Why do I have to write 20 words for this? This is why I’m rambling.
F (1) = -2
hope this helps :)

will be increasing on the intervals where

and decreasing wherever

. Local extrema occur when

and the sign of

changes to either side of that point.

is positive when

is between -4 and some number between -2 and -1, and also 2 (exclusive) and 4, so you can estimate that

is increasing on the intervals [-4, -2] and (2, 4].

is negative when

is between some number between -2 and -1, up to some number less than 2. So

is decreasing on the interval [-1, 1].
You then have two possible cases for extrema occurring. The sign of

changes for some

between -2 and -1, and again to either side of

.
I've actually just learned this. We would set up the proportion as X/9=36/X so after we cross multiply we get x^2=324. Then we find the square root of both sides to simplify. And using my calculator the square root of x^2 is just x. And the square root of 324 is 18. So the final answer is x=18 or the geometric mean is 18.