Process Costing BPP Question

Good Afternoon, D Co produces a certain food item in a manufacturing process. On 1 November, there was no opening inventory of work in process. During November, 500 units of material were input to the process, with a cost of $9000. Direct labour costs in November were $3840. Production overhead is absorbed at the rate of 200% of direct labour costs. Closing inventory on 30 November consisted of 100 units which were 100% complete as to materials and 80% complete as to labour and overhead. There was no loss in process. What is the full production cost of completed units during November? The answer is 16800. Please can you explain how this was answered? Ellis Co uses process costing to value its output. The following was recorded for the period: Input Materials 2000 units at $4.50 per unit Conversion costs 13,340 Normal Loss 5% of input valued at $3 per unit Actual loss 150 units There was no opening or closing inventories. What was the valuation of one unit of output to one decimal place? Input costs = 2000 units x $4.50 = $9000 Conversation costs = $13340 Normal Loss = 5% x 2000 units x $3 = $300 Expected output = 2000 units - 100 units = 1900 units Please can you explain where the 100 units came from? Thanks