Brook's is a specialty retailer of souvenir wear. Currently, the firm offer T-shirts, sweatshirts, and caps. Its most recent annual sales consisted of $23,300 of T-shirts, $9,600 of sweatshirts, and $2,800 of caps. The company is adding polo shirts to the line-up and projects that this addition will result in sales next year of $17,500 of T-shirts, $12,900 of sweatshirts, $16,100 of polo shirts, and $3,200 of caps. What amount of next year's revenue is from side effects of the additional product?