13. Two costs at Dickinson, Inc. appear below for specific months of operations. Month Amount Units Produced Janitorial January $42,000 40,000 February 42,000 60,000 March 42,000 54,000 Maintenance January $84,000 40,000 February 126,000 60,000 March 113,400 54,000 Which type of costs are these? a. Janitorial costs are variable and maintenance are fixed. O b.Janitorial costs are fixed and maintenance are variable. C. Both maintenance and janitorial are mixed. d. Janitorial costs are fixed and maintenance are mixed