please help me with this. don't mind the 25% because it's not part of the problem.

In each case, use the following information to calculate the missing information: 25% Case 1 Case 2 Case 3 Gross sales $ 640,000 $? $? Sales discounts 25,600 19,200 Sales returns and allowances 19,200 44,800 32,000 Net sales 608,000 1,209,600 ? Merchandise inventory, January 1 256,000 ? 384,000 Purchases 384,000 768,000 Purchase discounts 7,680 13,440 12,800 Purchase returns and allowances 24,320 31,360 32,000 Net purchases 352,000 ? 672,000 Transportation-in 25,600 38,400 32,000 Net cost of purchases 377,600 761,600 Cost of goods available for sale ? 1,081,600 1,088,000 Merchandise inventory, December 31 ? 384,000 448,000 Cost of goods sold 320,000 ? 640,000 Gross margin ? 512,000 320,000