please show all the formulas used step by step

6. During the month of May, Cassidy Manufacturers incurred $30,000, $40,000 and $20,000 of direct material, direct labor and manufacturing overhead costs respectively. If the cost of goods manufactured was $95,000 and the ending work in process inventory was 15,000, the beginning inventory of work in process must have been: a $10,000 b. $20,000 c. $110,000 d. $5,000 e. None of the above