Dakota Corporation provided the following information regarding its only product: Sales price per unit $60; DM used $160,000; DL incurred $230,000; Variable manufacturing overhead $150,000; variable selling and administrative expenses $60,000; fixed manufacturing overhead $80,000; fixed selling and administrative expenses $10,000; units produced and sold $12,000; assume no beginning inventory. Assuming there is excess capacity, what would be the effect on operating income of accepting a special order for $1,000 units at a sale price of $40 per product? (NOTE: Assume regular sales are not affected by the special order.) a) decrease by $10,000; b) decrease by $15,000; c) increase by $10,000; d) increase by $80,000