LICO uses the periodic method and weighted-average costing. On December 31, 20X7, LiCo's inventory consists of 1,800 units costing $5 each. In January, 20X8, LiCo purchases 4,000 units @ $9, of which it returns 700 units in March. It purchases 4,400 units in October @ $7. of which it returns 500 units in December. The weighted-average cost per unit of goods available for sale during 20X8 is. ... a. $7.92 b. $7.33 c. $6.47 d. $6.79