boersma sales, incorporated, a merchandising company, reported sales of 7,100 units in september at a selling price of $682 per unit. cost of goods sold, which is a variable cost, was $317 per unit. variable selling expenses were $44 per unit and variable administrative expenses were $22 per unit. the total fixed selling expenses were $157,200 and the total administrative expenses were $338,000. the contribution margin for september was: