Answer: Option (4) is correct.
Explanation:
No units in the beginning work in process inventory, so materials are added its full value means 100 percent in the beginning. Since, materials with 80,000 units were started the expense, it also includes ending work in process inventory. It is irrelevant for material cost to takes into account the percentage of completion of ending goods.
Therefore, 80,000 equivalent units of production for materials for the month of January.