Johnson Company operates two plants, Plant A and Plant B. Johnson Company reproted 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 totaled $50,000. Johnson Company's common fixed costs for last year were:

a. $50,000

b. $70,000

c. $40,000

d. $90,000