Assume the following information for one of a company's variable expenses: - The activity varlance is $710 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: Multple Choice $7.40 per hour $8.10 per hour: $7.10 per hour. $6.40 per hour