Sheffield Bookstore had 470 units on hand at January 1, costing $8 each. Purchases and sales during the month of January were as follows: Sheffield does not maintain perpetual inventory records. According to a physical count, 320 units were on hand at January 31. The cost of the imventory at January 31 , under the FIFO method is: $3240. $2560. $3660. $3370