Kingsport containers company makes a single product that is subject to wide seasonal variations in demand. the company uses a job-order costing system and computes plantwide predetermined overhead rates on a quarterly basis using the number of units to be produced as the allocation base. its estimated costs, by quarter, for the coming year are given below: quarter first second third fourth direct materials $ 240,000 $ 120,000 $ 60,000 $ 180,000 direct labor 128,000 64,000 32,000 96,000 manufacturing overhead 300,000 220,000 180,000 ? total manufacturing costs (a) $ 668,000 $ 404,000 $ 272,000 $ ? number of units to be produced (b) 80,000 40,000 20,000 60,000 estimated unit product cost (a) ÷ (b) $ 8.35 $ 10.10 $ 13.60 $ ?