Hi

I need help on the following question:

1) A symmetrical gutter is made of metal sheeting 30cm. wide by bending it twice as shown in the cross section. Find an expression for the area $\displaystyle A(\theta)$ of the cross section and hence find the value of $\displaystyle \theta$ for the gutter to have maximum carrying capacity.

http://img94.imageshack.us/img94/2024/diagramit.jpg
This is what i have try to do so far.

I know that Area of a square is L*W and Area of 2 triangles is $\displaystyle 2(0.5*x^2 * sin(\theta))$