Vaughn Inc uses the perpetual inventory system and the weighted average cost formula to value inventories. On August 1, there were 4000 units valued at $12000 in the beginning inventory. On August 10, 8000 units were purchased for $6 per unit. On August 15, 8000 units were sold for $10 per unit. The amount charged to cost of goods on August 15 was $36000. $40000 $48000 $28000