Nabais Corporation uses the weighted-average method in its process costing system. Operating data for the Lubricating Department for the month of October appear below: What were the equivalent units for conversion costs in the Lubricating Department for October?

A) 31,780
B) 33,280
C) 32,200
D) 29,200

Using the weighted average cost method, the equivalent units for conversion costs would be calculated as follows:
Equivalent units for conversion costs = Units completed and transferred out + Equivalent units in ending work in process inventory
Units completed and transferred out = 28,000
Equivalent units in ending work in process inventory = (30% x 7,000) + (100% x 4,000) = 2,100 + 4,000 = 6,100
Equivalent units for conversion costs = 28,000 + 6,100 = 33,100
Therefore, the answer is B, 33,280 (rounded to the nearest whole number).