What is the variable manufacturing overhead static-budget variance given the following information? Actual output units produced 28,000 units Actual machine hours used 10,000 hours Actual variable manufacturing overhead costs $300,000 Budgeted variable manufacturing overhead costs $250,000 Budgeted output units 25,000 units a) S50,000 unfavourable b) $20,000 unfavourable OC) $20,000 favourable Od) $50,000 favourable