I have a doubt with part D of the above mentioned question in the bpp revision kit. From the lecture, you said that parallel line can be drawn from the contribution line up to the point on the graph which gives the optimum production plan. However I am confused whether to choose the intersection of the line W and line F or line W and line T.
If the maximum demand for W falls to 200 units instead of 400 units, then line P on the graph will move closer to the original and instead of being a vertical line through 400 units it will be a vertical line through 200 units. Since this will obviously be to the left go point B on the graph, the optimum mix will be where the new line P (the W constraint) intersects with line F.