What is the long-run average cost of producing 30 units of output? Refer to the following table which shows three short-run cost schedules for three plants of different sizes that a firm might build in the long run. Plant 1 Plant 2 Plant 3 Output ATC Output ATC Output ATC 10 $10 10 $15 10 $20 20 9 20 10 20 15 30 8 30 7 30 10 40 9 40 10 40 8 50 10 50 14 50 9 Multiple Choice $9 $8 $7 $10