The Northern Co. manufactures office chairs. The following information is available for June: Selling price per chair $140 Variable cost per chair 90 Total fixed costs 105,000 If the company sells 1,500 chairs in the month of June, the margin of safety in units is .(Round-off the answer to the nearest whole number.) O a. -619 chairs b. -600 chairs O c. -609 chairs O d. -629 chairs