KIM Manufacturing recorded operating data for its auto accessories division for the year. Sales $750,000 Contribution margin 150,000 Total direct fixed costs (controllable) 90,000 Average total operating assets 450,000 How much is ROI for the year if management is able to identify a way to improve the contribution margin by $30,000, assuming fixed costs are held constant? 18.0% . 22.8% Ob. 20.0% Oc 12.0%