Calculate the missing numbers in the following situations. (Input all amounts as positive values.) Invoice cost of merchandise purchases $ a b 45,000 $ 22,000 $ 17,250 Purchase discounts 3,000 375 Purchase returns and allowances 2,000 850 650 Cost of transportation-in 2,250 3,000 Merchandise inventory (beginning of period) 5,500 4,500 Net cost of merchandise purchases 45,700 20,250 Merchandise inventory (end of period) 2,700 4,250 Cost of goods sold $ 21,800 $ 18,065