Compute the company's predetermined overhead rate. 38. Chapter 4: Trapp Corporation uses the weighted-average method in its process costing system. The beginning work in process inventory in its Painting Department consisted of 3,000 units that were 70% complete with respect to materials and 60% complete with respect to conversion costs. The cost of the beginning work in process inventory in the department was recorded as $10,000. During the period, 9,000 units were completed and transferred on to the next department. The costs per equivalent unit for the period were $2.00 for material and $3.00 for conversion costs.