Birkner Corporation's flexible budget performance report for last month shows that actual indirect materials cost, a variable cost, was $30,444 and that the spending variance for indirect materials cost was $8,142 favorable. During that month, the company worked 17,700 machine-hours. Budgeted activity (i. e., planning budget activity) for the month had been 18,200 machine-hours. The budgeted cost formula per machine-hour for indirect materials cost must have been closest to: