Seabold Interiors sold 18,400 yards of wallpaper last year at a contribution margin of $3.50 per yard and incurred $49,400 in total fixed costs. This year contribution margin per yard is expected to increase to $4, and fixed costs are expected to increase to $58,000. How many units must be sold this year to earn the same operating income as was earned last year? (Hint: Use the expanded contribution margin model described in this chapter. ) a. 16,900. b. 17,500. c. 18,250. d. 20,200. e. None of the above