the answer is b can you explain how please.

Mixed bank 5 33.1 A firm has the following transactions with its product R. 1 January 20X1 Opening inventory: nil 1 February 20X1 Buys 10 units at $300 per unit 1 1 February 20X1 Buys 12 units at $250 per unit 1 April 20X1 Sells 8 units at $400 per unit 1 August 20X1 Buys 6 units at $200 per unit 1 December 20X1 Sells 12 units at $400 per unit The firm uses FIFO to value its inventory. What is the inventory value at the end of the year? $nil $1,700 $2,400 $2,007.20