15-18B. (Fixed costs) Tropical Sun projects that next year its fixed costs will total $135,000. Its only product sells for $13 per unit, ofwhich $6 is a variable cost. The management ofTropical is consider·

ing the purchase of a new machine that will lower the variable cost per unit to $5. The new machin~

however, will add to fixed costs through an increase in depreciation expense. How large can the addition to fixed costs be to keep the firm's break-even point in units produced and sold unchanged?