The following standards for variable manufacturing overhead have been established for a company that makes only one product: Standard hours per unit of output 2.7 hours Standard labor rate $13.05 per hour The following data pertain to operations for the last month: Actual hours 2.400 hours Actual total variable manufacturing overhead cost $30.360 Actual output 600 units What is the variable overhead efficiency variance for the month? $9,219 U $10,179 U $9,867 U $648 U