If the price of a commodity is directly proportional to m3 a

[vkt219]

ok, so, basically, you are just using the formula that's given in the first post (km^3 / q^2), but you've chosen k = 1.
this is fine, of course.

...but, how are you getting C as an answer?

C gives 20.
D gives MORE than 20.
you want the biggest answer.

huh?

Thanks for pointing out the typo. Corrected. My biggest concern with the question is that the answer choices change the Ascending pattern midway (post D it decreases). Is this pattern also repeated in OG problems (or the real GMAT)?

[RonPurewal]

there's no such "pattern" in HOW THE ANSWERS TURN OUT... i mean, of course there isn't! (:
you're not thinking this one through...
if the answer choices were ordered in terms of increasing or decreasing OUTCOME, then you could conclude right away that the answer would have to be either A or E, without even doing anything!
clearly, the problem isn't going to work that way.

when the answer choices are single numbers, they'll be arranged in increasing or decreasing order -- mainly for reasons of convenience. this has absolutely nothing to do with the outcomes of the problems (which the authors are pretty good at randomizing).