I don't understand why the answer is 1800. Can someone explain to me why it's not just (200 * 4)+(800*4.25)?

Snow Company has the following inventory transactions for the year: Unit Numbers of Units 200 Date Jan. 1 Transaction Beginning inventory Purchase Purchase Cost $4.00 4.25 4.50 800 Apr. 20 Sep. 8 400 Assuming Snow sells 1,000 units, calculate ending inventory under FIFO. Multiple Choice $1,650. $1,800. $4,200. $4,350