Answer:
January 1, 2020, inventory was $334,640 at both cost and market value.
December 31, 2020, the inventory was $425,820 at cost and $400,440 at market value.
When using lower of cost or market value, we must record our inventory at whichever is lower. The total loss of inventory value = $425,820 - $400,440 = $25,380.
a) the cost-of-goods-sold method
December 31, adjustments to record loss on inventory's market value.
Dr Cost of goods sold 25,380
Cr Inventory* 25,380
b) loss method
December 31, adjustments to record loss on inventory's market value.
Dr Loss due to decline of inventory to market value 25,380
Cr Inventory* 25,380
*Depending on what account you are told to use (instead of inventory account) you might be required to use the Allowance to reduce inventory to market value account.