can somone explain the correct ans option?

Question 7 Which of the following is the correct mathematical expression to calculate the fixed manufacturing overhead production-volume variance? O a. The static-budget amount minus the flexible-budget amount for the fixed manufacturing overhead. O b. The flexible-budget amount minus the actual amount incurred for the fixed manufacturing overhead. O c. The actual fixed manufacturing overhead amount incurred minus the fixed manufacturing overhead amount allocated for actual output. O d. The budgeted fixed manufacturing overhead amount minus the fixed manufacturing overhead amount allocated for actual output. O e. None of the answers