The level of inventory of a manufactured product has increased by 7,908 units during a period. The following data are also available: Variable Fixed Unit manufacturing costs of the period $10.00 $7.00 Unit operating expenses of the period 3.00 2.00 The effect on operating income if variable costing is used rather than absorption costing would be a(n) a. $71,172 decrease b. $55,356 decrease c. $55,356 increase d. $71,172 increase