BPP Practice & Revision Kit 8a.11 page 63

Hi Sir, Please can you help me with the following question: A company uses process costing to establish the cost per unit of its output. The following information was available for the last month: Input units 10,000 Output units 9,850 Opening inventory 300 units, 100% complete for materials and 70% complete for conversion costs Closing inventory 450 units, 100% complete for materials and 30% complete for conversion costs The company uses weighted average method of valuing inventory. What were the equivalent units for conversion costs? A 9,505 units B 9,715 units C 9,775 units D 9,985 units BPP shows the answer is D. I think it's C as we need to minus the opening inventory (300*70%) as it's not produced during this process. Many Thanks