1. Calculate the weighted-average contribution margin. 2. Determine 's monthly breakeven point in dozens of plain donuts and custard-filled donuts. Prove your answer by preparing a summary contribution margin income statement at the breakeven level of sales. Show only two categories of costs: variable and fixed. 3. Compute 's margin of safety in dollars for . 4. Compute the degree of operating leverage for Donuts. Estimate the new operating income if total sales increase by . (Round the degree of operating leverage to four decimal places and the final answer to the nearest dollar. Assume the sales mix remains unchanged.) 5. Prove your answer to Requirement 4 by preparing a contribution margin income statement with a increase in total sales. (The sales mix remains unchanged.)