Q: A trough is to be made from three planks, each 12 in. wide. If the cross section has the shape of a trapezoid, how far apart should the tops of the sides be placed to give the trough maximum carrying capacity? OK the area of a trapezoid is A=2bh I know that much, but I've been struggling with this one, off and on, for about two days. I just don't know where to start. I'm not looking for an answer, just a starting point please.