Economic rent is earnings in excess of what?

Computer memory chips are produced on wafers, each wafer having many separate chips that are separated and sold. The above table shows costs for a perfectly competitive producer of computer memory chips

If the market price of a wafer is $2,400 dollars, how many wafers will the firm produce? A) 0 B) 4 or 5 C) 3 or 4 D) 1 or 2 E) 6

At the point at which P=MC, suppose that a perfectly competitive firm's MC = $100, its AVC = $80 and its AC = $110. This firm should

A) shut down immediately. B) continue operating in the short run. C) try to take advantage of economies of scale. D) try to increase its advertising and promotion.