4. A firm manufactures cars at its plant in Swindon. At a capacity of 100 cars per week it knows that it has an assembly cost of $5,000 per car. It needs to expand production and does a series of design and cost exercises. The results are summarised below. Output (cars 200 400 600 800 1,000 1,200 1,400 1,600 per week) Assembly 3,000 2,500 2,300 2,200 2,000 2,400 2,800 4,000 cost (f per car) a) Plot the cost curves for the possible factory extensions. b) Is this a short run or long run cost curve? c) Explain why this curve is U shaped