Where did our ending inventory value come from- discussion

On the income statement at the end of the year (using the periodic system of inventory costing) how did the controller determine the value of ending work in process inventory? You might have to think this one out as the book doesn't really explain it.

Hint: Don't tell me that you subtract total cost of goods manufactured by total manufacturing costs. Why? You first need to calculate ending work in process to find cost of goods manufactured. Sort of like what came first the chicken or the egg!