The University Store, Incorporated is the major bookseller for four nearby colleges. An income statement for the first quarter of the year is presented below: University Store, Incorporated Income Statement For the Quarter Ended March 31 Sales Cost of goods sold Gross margin Selling and administrative expenses Selling Administrative Net operating income $ 100,000 110,000 $ 800,000 560,000 240,000 210,000 $ 30,000 On average, a book sells for $40.00. Variable selling expenses are $3.00 per book; the remaining selling expenses are fixed. The variable administrative expenses are 5% of sales; the remainder of the administrative expenses are fixed. The cost formula for selling and administrative expenses with "X" equal to the number of books sold is: