Baxter Corporation's master budget calls for the production of 5,800 units per month and $222,720 indirect labor costs for the year. Baxter considers indirect labor as a component of variable factory overhead cost. During April, the company produced 4,580 units and incurred indirect labor costs of $12,900. What amount would be reported in April as a flexible-budget variance for indirect labor? Is this variance favorable (F) or unfavorable (U)? (Leave no cell blank; if there is no effect enter "O" and select "None" from dropdown. Do not round intermediate calculations.)