Answer: The correct answer is "d. $24,000".
Step-by-step explanation: The balance in the work-in-process inventory on December 31 is equal to $ 24,000.
First we must calculate the manufacturing costs of the period = Direct materials + Direct labor + Factory Overhead = 68000 + 66000 + 90000 = 224000.
Secondly, we must add to the manufacturing costs of the period the initial existence of work in progress = 224000 + 30000 = 254000
Finally we subtract the Cost of goods manufactured that is $ 230,000 = 254000 - 230000 = $24000.