The following standards for variable manufacturing overhead have been established for a company that makes only one product: Standard hours per unit of output........ Standard variable overhead rate .......... 4.2 hours $11.55 per hour The following data pertain to operations for the last month: Actual hours ............. Actual total variable manufacturing overhead cost....... Actual output........... 8,600 hours $95,890 1,900 units What is the variable overhead efficiency variance for the month? $3,192 U O $6,913 F $7,161 U $6,913 U