Why is average cost and short run marginal cost always u-shaped

World systems manufactures an optical switch that it uses in its final product. world systems incurred the following manufacturing costs when it produced 74 comma 000 units last​ year: ​(click the icon to view the manufacturing​ costs.) another company has offered to sell world systems the switch for $ 13.50 per unit. the world systems prepared an outsourcing decision analysis to show the cost per unit of making the switches versus the cost per unit of buying​ (outsourcing) the switches. ​(click the icon to view the outsourcing decision​ analysis.) world systems needs 86 comma 000 optical switches next year​ (assume same relevant​ range). by outsourcing​ them, world systems can use its idle facilities to manufacture another product that will contribute $ 140 comma 000 to operating​ income, but none of the fixed costs will be avoidable. should world systems make or buy the​ switches? show your analysis.