STEP-BY-STEP ANSWER:
Step 1: Identify the historical cost of the inventory item, which is $600.
Step 2: Determine the current market value of the inventory item, which is $550.
Step 3: Compare the cost and market values.
Step 4: Select the lower value. In this case, $550 is less than $600.
Final Answer: The inventory should be valued at $550.