HiTech manufactures two products: Regular and Super. The results of operations for 20x1 follow. Fixed manufacturing costs included in cost of goods sold amount to $3 per unit for Regular and $20 per unit for Super. Variable selling expenses are $4 per unit for Regular and $20 per unit for Super; remaining selling amounts are fixed.

43. HiTech wants to drop the Regular product line. If the line is dropped, company-wide fixed manufacturing costs would fall by 10% because there is no alternative use of the facilities. What would be the impact on operating income if Regular is discontinued? A. $0. B. $10,400 increase. C. $20,000 increase. D. $39,600 decrease. E. None of these.

The answer is D however I need to know how to arrive at that answer. Thank you!