The following data pertain to Turk Company's operations last year: Sales$ 900,000 Net operating income $ 36,000 Contribution margin$ 150,000 Average operating assets $ 180,000 Stockholders' equity $ 100,000 Plant, property, & equipment $ 120,000 If the residual income for the year was $9,000, the minimum required rate of return must have been: A) 15% B) 4% C) 20% D) 36%