Causwell company began 2018 with 10,000 units of inventory on hand. the cost of each unit was $5.00. during 2018 an additional 30,000 units were purchased at a single unit cost, and 20,000 units remained on hand at the end of 2018 (20,000 units therefore were sold during 2018). causwell uses a periodic inventory system. cost of goods sold for 2018, applying the average cost method, is $115,000. the company is interested in determining what cost of goods sold would have been if the fifo or lifo methods were used.