A manufacturer of fine pens produces in two plants. The total cost of producing in the first plant is given by TC1=y21 100 . The total cost of producing in the second plant is given by TC2=y323 200 . In these cost functions, y1 corresponds to the number of pens produced in the first plant, and y2 corresponds to the number of pens produced in the second plant. Suppose the firm is producing 180 fine pens. If the firm is minimizing costs, it must be producing pens in the first plant