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 Direct labor Manufacturing overhead Total manufacturing costs (a) Number of units to be produced (b) $280,000 $140,000 $ 70,000 $210,000 80,000 40,000 20,000 60,000 230,000 206,000 194,000 ? $590,000 $386,000 $284,000 $ ? 120,000 60,000 30,000 90,000 Estimated unit product cost (a) + (b) $ 4.92 $ 6.43 $ 9.47 $ ? Management finds the variation in quarterly unit product costs to be confusing and difficult to work with. It has been suggested that the problem lies with manufacturing overhead because it is the largest element of total manufacturing cost. Accordingly, you have been asked to find a more appropriate way of assigning manufacturing overhead cost to units of product.