21. Given the following information, determine the cost of ending inventory at December 31 using the perpetual inventory methood. December 2: 5 units were purchased at $7 per unit. December 9: 10 units were purchased at $9.40 per unit. December 11: 12 units were sold at $35 per unit. December 15: 20 units were purchased at $10.15 per unit. December 22: 18 units were sold at $35 per unit a. $51.75 b. $83.22 c. $41.30 d. $94.00 e. $50.75