The following is last month's contribution format income statement: Sales (15,000 units) ...... 1,500,000 Variable expenses ......... 900,000 Contribution margin ....... 600,000 Fixed expenses ............. 500,000 Net operating income ..... 100,000 What is the company's margin of safety in dollars? a. $100,000 b. $600,000 c. $1,500,000 d. $250,000