Revenues $4,500 Variable manufacturing costs $900 Variable nonmanufacturing costs $810 Fixed manufacturing costs $630 Fixed nonmanufacturing costs $545 Required: a. Compute contribution margin. A. $2,500 B. $2,790 C. $2,300 D. $2,900 b. Compute contribution margin percentage. A. 67% B. 55% C. 62% D. 69% c. Compute gross margin. A. $3,500 B. $3,400 C. $2,550 D. $2,790 d. Compute gross margin percentage. A. 65% B. 60% C. 77% D. 66% e. Compute operating income