Optimization problem?

an architect has been asked to design a Norman window for a small office space, to add interest and light. A Norman window is constructed by adjoining a semicircle to the top of an ordinary rectangle. This window will have special decorative trim purchased by linear foot, so it will pay to get the most light for the least perimeter of window. If 10 feet of trim is allotted for the Norman window (including the segment between the semicircle and the rectangle), what dimensions will maximize the area?