Johnson Company operates two plants: Plant A and Plant B. Johnson Company reported for the year just ended a contribution margin of $50,000 for Plant A. Plant B had sales of $200,000 and a contribution margin ratio of 30%. Net operating income for the company was $20,000 and traceable fixed costs for the two plants totalled $50,000. What were Johnson Company's common fixed costs for last year? Select one: a. $90,000. b. $70,000. c. $40,000. d. $50,000