Skafic Corporation, a smartphone manufacturer, normally produces and sells between 10,000 and 15,000 units per year. The following cost data apply to various activity levels. Change Number of Units 10,000 12,000 14,000 15,000 Total costs incurred Fixed $75,000 Variable 100,000 Total costs $175,000 Cost per unit Fixed Variable $ 7.50 10.00 Total cost per unit $17.50 Required a. Complete the preceding table by filling in the missing amounts for the levels of activity shown in the first row of the table. Round all cost-per-unit figures to the nearest whole penny. b. Explain why the total cost per unit decreases as the number of units increases.