Question on valuing opening work in progress: FIFO method

Hi, If anyone could please help me with the question from BPP F2 Study Guide. Walter Co uses the FIFO method of process costing. At the end of a four-week period, the following information was available for process P. Opening WIP 2000units (60% complete) costing $3000 to date Closing WIP 1500units (40% complete) Transferred to next process 7000units How many units were started and completed during the period? A) 5000units B) 7000units C) 8400units D) 9000units It seems to me that none of the answers is correct. My reasoning: Total output = 2000+7000 - 1500 = 7500 Less opening WIP (completed first) 2000 Thus the answer should be 5500units. Or would it be 2000x0.4 (800units) + 1500x0.4(600units) + 5500units= thus 6900 units? Would appreciate any help on this.