The Rutherford Company's costs and activity level for April and May are as follows: May. Activity level in units April 10,000 20,000 Variable costs Fixed costs Mixed costs Total costs $10,000 30,000 20,000 $60,000 ? $75,000 Assuming that these levels are within the relevant range, the cost function for the company's total costs is Select one: A. Total costs = $60,000 + $0.50 Units