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Optimization Problem
Having a bit of trouble with what should be a fairly simple problem. Unfortunately it's been a while since I've done any of this stuff so I was wondering if any of you could help me out.
You really need to see the diagram to understand the question so I've uploaded the problem here: tinypic.com/r/5ckej5/5 (I've also attatched it)
Now in part a) it's obvious that to get the answer your simply multiplying y=9(1/4)x^2 by 2x. What I don't understand is how that would give you the area of the cuboid.
Any help would be much appreciated thanks :).

To get the *volume* you need to multiply the *area* (in part A) by 60m (distance between first and last arch).
They're asking you to find x so that the area (and hence the volume) is maximized. So you take a derivative, set it equal to zero...