Universal Manufacturing uses a weighted-average process-costing system. All materials are introduced at the start of manufacturing, and conversion costs are incurred evenly throughout the process. The company's beginning and ending work-in-process inventories totaled 10,000 units and 15,000 units, respectively, with the latter units being 2/3 complete at the end of the period. Universal started 30,000 units into production and completed 25,000 units. Manufacturing costs follow. Beginning work in process: Materials, $60,000; conversion cost, $150,000Current costs: Materials, $180,000; conversion cost, $480,000Universal's equivalent-unit cost for materials is:a. $4.50.b. $6.00.c. $8.00.d. $9.60.e. some other amount.