The following standards for variable overhead have been established for a company that makes only one product: Standard hours per unit of output. ......... 6.3 hours Standard variable overhead rate. $18.65 per hour The following data pertain to operations for the last month: Actual hours ....... 8,600 hours Actual total variable overhead cost. $157.380 Actual output ........ 1.100 units What is the variable overhead efficiency variance for the month? Select one: O a. $28,136 U O b. $31,146 U O c. $30,561 U O d. $2,426 U