Given the following information, determine the cost of goods sold at December 31 using the Weighted Average periodic inventory method. December 2: 22 units were purchased at $8.70 per unit. December 9: 27 units were purchased at $11.10 per unit. December 11: 29 units were sold at $36.70 per unit. December 15: 37 units were purchased at $11.85 per unit. December 22: 35 units were sold at $36.70 per unit.