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