Walsh Automobile Company fabricates automobiles. Each vehicle includes one airflow sensor, which is currently made in - house. Details of the airflow sensor fabrication are as follows: Volume Variable cost per unit Fixed costs 800 units per month $7 per unit $13,000 per month A Japanese factory has offered to supply Walsh with ready-made units for a cost of $15 per sensor. Assume that Walsh's fixed costs could be reduced by $4,000 if it outsources and that Walsh will not be able to use the excess capacity in any profitable manner. If Walsh decides to outsource, monthly operating income will: OA. increase by $13,000 OB. increase by $5,600 C. decrease by $2,400 D. decrease by $13,000