4. Keelung Company adopts the periodic inventory system. At the beginning of 20X1, the inventory is $30,000, and the inventory value is $45,000 according to the final inventory. On December 31 of that year, the company has net sales revenue of $310,000. purchase of $240,000, purchase discount of $4,000, purchase returns and allowances of $5,500. purchase freight $8,000. Please calculate the cost of goods sold and gross profit of Keelung company in year 20X1. (10%)