stolyar
No problem, Sir
You have to bend your metal sheet in some way, to have a П-shaped object. Since, the lenght is not important, concentrate on a П-section.
A section of maximal area will give you maximal volume.
So, how to bend a 12' line in 3-side, П-object to cover the maximal area?
Imagine a rectangular with sides: X, X, 12тАУ2X, 12тАУ2X. Let X be a vertical side, and 12тАУ2X be a horizontal one.
X+X+12тАУ2X=given 12 and one side is virtual
An area of the section is X*(12тАУ2X)= 12XтАУ2X^2
A derivative is 12тАУ4X=0, where X=3
so your gutter should have two 3' vertical sides and one 6' horizontal.
Such section gives you 18 square inch area
All others are smaller (10+1+1) gives 10
(8+2+2) gives 16
(4+4+4) gives 16
With the same perimetr a circle has the smallest area, but a square -- the greatest.
An area of the section is X*(12тАУ2X)= 12XтАУ2X^2
A derivative is 12тАУ4X=0, where X=3
This does not look correct!