Assume the following information for one of a company's variable expenses: The activity variance is $860 favorable. The actual amount of the expense is $8,300. The planned level of activity is 1,000 hours. The actual level of activity is 900 hours. . . The cost formula for this expense must be: Multiple Choice $8.60 per hour. $8.90 per hour. $9.60 per hour. $7.90 per hour