Question 1: Contribution format income statement and High-Low Method The accounting department of Blackwell Pty Ltd, a merchandising company, has prepared the following analysis: Cost Cost Formula Cost of goods sold $67 per unit Sales commissions Advertising expense Administrative salaries Billing expense Depreciation expense 15% of sales $400,000 per month $200,000 per month ? $95,000 per month The accounting department feels that billing expense is a mixed cost, containing both fixed and variable cost elements. The billing expenses and sales in units over the last several months follow: Units Sold (thousands) Billing Expense January 13 $39,000 February 11 $37,000 March 16 $42,000 April 17 $44,000 May 19 $47,000 June 14 $41,000